Genesis 18:21 (KJV) states:
I will go down now, and see whether they have done altogether according to the cry of it, which is come unto me; and if not, I will know.
If God is all knowing, why did he have to come down to earth to see if what he had heard about the evilness going on in Sodom was true?
God does this for the sake of mankind, not His own. Take, for instance, Gen 3 and The Fall. Adam and Even have sinned and God comes walking around, looking for them because they had hidden themselves. Did God know where to find them? Absolutely. He could have just appeared behind them and made it clear their efforts were futile from the start. But He clearly wanted them to feel like they could hide from him physically. He let them experience that futility first-hand.
The section of Gen 18 you're referencing is where God has just told Sarah she will have a child. He then turns towards Sodom and tells Abraham he is about to wipe it out. Abraham pleads with God directly, bargaining Him down to where if 10 righteous people can be found, God will not wipe out the area (spoiler alert: He doesn't). But the reason he's saying all this in person is for Abraham's benefit. Gen 18: 17-19 makes that clear
17 The Lord said, “Shall I hide from Abraham what I am about to do, 18 seeing that Abraham shall surely become a great and mighty nation, and all the nations of the earth shall be blessed in him? 19 For I have chosen him, that he may command his children and his household after him to keep the way of the Lord by doing righteousness and justice, so that the Lord may bring to Abraham what he has promised him.”
There's two points about this
We see a similar dynamic in Exodus 32. The Israelites have built the golden calf and are running wild.
7Then the Lord said to Moses, “Go down, because your people, whom you brought up out of Egypt, have become corrupt. 8They have been quick to turn away from what I commanded them and have made themselves an idol cast in the shape of a calf. They have bowed down to it and sacrificed to it and have said, ‘These are your gods, Israel, who brought you up out of Egypt.’
9“I have seen these people,” the Lord said to Moses, “and they are a stiff-necked people. 10Now leave me alone so that my anger may burn against them and that I may destroy them. Then I will make you into a great nation.”
11But Moses sought the favor of the Lord his God. “Lord,” he said, “why should your anger burn against your people, whom you brought out of Egypt with great power and a mighty hand? 12Why should the Egyptians say, ‘It was with evil intent that he brought them out, to kill them in the mountains and to wipe them off the face of the earth’? Turn from your fierce anger; relent and do not bring disaster on your people. 13Remember your servants Abraham, Isaac and Israel, to whom you swore by your own self: ‘I will make your descendants as numerous as the stars in the sky and I will give your descendants all this land I promised them, and it will be their inheritance forever.’ ” 14Then the Lord relented and did not bring on his people the disaster he had threatened.
Did God really need Moses to talk him out of wiping the Israelites out? Of course not! God tells Moses this so Moses would remind himself of why God won't wipe them out. And Moses needs that reminder, because he's about to deal with this problem again and again.
And there came two angels to Sodom at even; [Genesis 19:1 KJV]
Justice and judgment require a true witness.
In the mouth of two or three witnesses let every matter be established. [Deuteronomy 19:15 KJV]
In order to judge with such unprecedented immediacy and such irrevocable consequences, God manifestly 'observes' (angelically) the true state of matters, in two visible witnesses.
And that very observation precipitates a state of affairs (the event of crowd-gathering and assault and threat) that justifies the shocking conflagration that follows upon the cities of the plain.
I will go down now, and see whether they have done altogether according to the cry of it, which is come unto me; and if not, I will know. [Genesis 18:21 KJV]
Note the opposite situation when Cain slew Abel but there was no witness and no confession. Cain is protected from unlawful retaliation in the absence of substantial evidence.
It was not because of a necessity concerning binding judicial process or lack of information that God sent angels to investigate. Consider Elihu's words in Job:
23 God has no need to examine people further,
that they should come before him for judgment.
24 Without inquiry he shatters the mighty
and sets up others in their place.
25 Because he takes note of their deeds,
he overthrows them in the night and they are crushed. (Job 34:23-25)
The important words in Genesis 18 are these:
16 Then the men set out from there, and they looked down toward Sodom. And Abraham went with them to set them on their way. 17 The Lord said, “Shall I hide from Abraham what I am about to do, 18 seeing that Abraham shall surely become a great and mighty nation, and all the nations of the earth shall be blessed in him? 19 For I have chosen him, that he may command his children and his household after him to keep the way of the Lord by doing righteousness and justice, so that the Lord may bring to Abraham what he has promised him.” (Genesis 18:16-19)
Consider the words of Amos in Amos 3:6-7:
6 Is a trumpet blown in a city,
and the people are not afraid?
Does disaster come to a city,
unless the Lord has done it?7 “For the Lord God does nothing
without revealing his secret
to his servants the prophets.
The investigation was part of God's work in elevating Abraham to the rank of prophet. God announces and explains his actions to the prophets so that they may communicate God's words and intention to the people.
God was moving towards establishing a legal framework to govern the relationship between him and Israel. The Law has many processes, rules and formalities that must be obeyed. God is teaching Abraham and those who follow how to build a civilization built on Law and Justice by His own example. God is our teacher.
A later example that adds additional motives for God is in Joshua:
7 The Lord said to Joshua, “Today I will begin to exalt you in the sight of all Israel, that they may know that, as I was with Moses, so I will be with you. (Joshua 3:7)
Right after this, the Lord stopped up the waters of the Jordan so that the people could pass over in safety. That act was God's miraculous endorsement of Joshua as His chosen representative.
In like fashion, giving Abraham advance warning about the destruction of Sodom and Gomorrah AND effecting the salvation of Abraham's nephew Lot was an act by which God began to exalt Abraham into a truly "exalted father".
There is another reason. The angels sent to investigate were the focus of a test. God did not destroy Sodom and Gomorrah, he destroyed them AND rescued Lot and his daughters. By risking his life to defend the "visitors", Lot proved his righteousness.
Jesus spoke in Parable about how a landowner sent out his servants to collect his share of the harvest but his servants were beaten or killed by the tenants. The poor welcome given to these three angels was an example of the murderous hearts of the tenants of this world. This story foretells what would happen to future agents of the gospel, but also the end that would come to those wicked tenants.
Here is a side-by-side translation from the Hebrew of Genesis 18:21. The "whether" in English is inferred, and is not explicit in the Hebrew text. The latter condition ("and if not") does appear to be an explicit condition, although its meaning relative to the rest of the text might not be perfectly clear.
There is not always a straightforward and unambiguous way to translate the Hebrew into English. Pronouns are often (but not always) seen as implicit, and articles are scarce. It can be difficult to piece together conditions as in this case, or what exactly is being inquired. Sometimes translators such as those of the KJV inferred and imputed an intent, which makes it seem obvious from the English but may not be as clear given our understanding of the Hebrew, especially where there may have been idiomatic expressions in the original. Idioms are naturally transparent except where they seem to have a jarring meaning or be out of place, but even then the meaning is not immediately apparent. The meanings of idioms which are usually inferred because of their occurrence in another context where the meaning is more obvious or due to their preservation in practically unchanged form in a more modern version of the language.
In short, lacking greater clarity in the text and resolution of any possible idioms, it might not be possible to state with 100% certainty that the verse in question refers to God descending personally as if to observe and acquire information confirming a prior report.
But taking a less dogmatic view of the principle, and speaking theologically broadly and inclusively, one can see it as not necessarily being the case that the omniscience of God is without Personal perception, or comprehended by inclusion of His messengers and ministering angels. The Scripture as rendered in the English does imply that God receives reports of some kind. It can also as Nigel suggests be an illustration of the law of witnesses.
"Omniscience" may also be an ill-defined concept generally; see this related question on the topic of omnipotence, showing a similar challenge of definition.
God coming to earth doesn't mean he doesn't have access to everything happening in the cosmos. Not only does God know what happens on earth, but in space and the rest of the creation. God knows how many times a tree has been blown by the wind since it was a seedling up to now. He has access to everything because he is in all and all is in him. His presence surpasses all understanding. That's why the prophets in my church know things that happened to me when I was a kid and yet they are strangers to me.
God knows whether the moon landings were real or faked. God knows if they were staged or they actually put their foot on the moon because you cannot lie to the Holy Spirit.
Ananias and Saphirah sold their land and kept some money back and tried to lie to the Holy Spirit(God) that it was all and they died
Firstly there are things God didn't know prior to coming to earth and Finding out personally. God didn't know fear, didn't know weakness or temptation. He knows facts but he does not know some things. He doesn't know how it feels to be the one that detests him. He doesn't know how it feels to believe he is a liar. God makes observations and uses then to make determinations, he learns. He created light. Looked upon it, and saw that it was good. Action/observation/determination. Not all of his questions are rhetorical. He genuinely gets sad and happy and angry and proud. Jesus was his solution to learning why humans inherently sin despite his commandments. He likely discovered the demand of the animal flesh compete with with spiritual demands of the soul and they are strong enough to cause a person to fail to obey him. Hence the resulting salvation that came from his experiencing human weakness first hand by being made flesh for a while.
FYI I worship God and Christ. That makes me a Christian. Therefore my beliefs are Christian. I dont require the Vatican to agree with me in order for my beliefs to be valid. Don't wrongly declare you have the authority to decide what is or isn't a Christian belief. There is more than one strict interpretation and none is truly superior to all others. Flaws in previous counterargument. Hebrew to English translational shortcomings aren't an effective argument, because in his perfect divinity he would hold the scripture to be perfect as the word of God right? So he would anticipate translational issues in advance and he would make it so that despite the compatibility issues involving turning ancient Hebrew into modern English it would be so that the message would somehow come out correctly. Otherwise your simply picking and choosing a narrative that supports your beliefs instead of basing your beliefs on the narrative provided. Personally i don't think that scripture is flawless, but that goes for ancient Jewish texts as well. The moment a human has to turn the thoughts in their head given by a revelation from God, words immediately fail to describe what is seen. I believe that God made sure that enough of the important stuff made it through for us to have a chance to grasp what we need to point in the right direction. I dont think that who begat who begat who begat who is absolutely vital to achieving a relationship with the creator. Even the scriptures had to be drastically dumbed down in order to be comprehended by humans across the span of thousands of years and hundreds of languages. Andvl still be universally relevant.
Anyhow my original answer begins here:
There is a much easier way to grasp alot of this stuff that most people don't grasp. Here are some suggestions that might enable you to better understand the situation.
God"I am because I am" he exists because he is aware he exists. He has limitless I power and such because existence itself Is a construct firmed by his own "mind" so to speak.
The many worlds theory is right but it's backwards, rather than the stupid way it's presented where each choice or "free will" action creates alternate timeliness is dumb. It actually works in the much more obvious and directly observable law called reality. Initially there are virtually unlimited possibilities, as the quantum state of everything is still undetermined, meaning anything is possible until it isnt. Your choice to be a janitor doesn't create a world in which you are a horse jockey instead. Rather it collapses and deletes any reality in which your not a janitor. It's a simple matter of which opportunities get utilized. Naturally everything everybody does affects the quantum state of our shared environment, so in that way every free willed creature alters everyone's universe with every choice they make. It's like quantum entanglement,observing something or deciding something quantum entangled that reality with the overall story line. Anything that disagrees with it isn't reality and therefore doesn't exist exept for as a hypothetical.
Because of this mechanism, the actions we take and all that really are an expression of free will, because we are not rigidly forced to obey our biochemical reward systems in our bodies the way many organisms are. We can arbitrarily opt to ignore our instincts and choose to do things counterintuitive, which is a trait fairly unique
