This should be considered the Holy Catholic Answer of Truth.
Why they think they would die if he spoke to them
Let us first understand this. Why is this nature of fear inside these Israelites? Let us look into the history of things to find this answer.
And they heard the sound of the Lord God walking in the garden in the cool of the day, and Adam and his wife hid themselves from the presence of the Lord God among the trees of the garden. 9 Then the Lord God called to Adam and said to him, “Where are you?” 10 So he said, “I heard Your voice in the garden, and I was afraid because I was naked; and I hid myself.” (Genesis 3:8-10 NKJV)
By this we can see that Adam once he ate of the fruit also had this fear. The natural response to eating of these fruits is to hide from the truth, and to place the blame on another.
And He said, “Who told you that you were naked? Have you eaten from the tree of which I commanded you that you should not eat?” 12 Then the man said, “The woman whom You gave to be with me, she gave me of the tree, and I ate.” 13 And the Lord God said to the woman, “What is this you have done?” The woman said, “The serpent deceived me, and I ate.” (Genesis 3:11-13 NKJV)
It is very important to understand this occurrence and how it continues through the generations. By this a true understanding of this fear, will explain why they sent Moses for them. So knowing exactly what the fruits of the Knowledge of Good and Evil are is necessary to completely understand this.
First it is not a literal fruit
But the fruit of the Spirit is love, joy, peace, longsuffering, kindness, goodness, faithfulness, 23 gentleness, self-control. Against such there is no law. (Galatians 5:22-23 NKJV)
The Hebrew meaning to the words Good and Evil
The Ancient Hebrew Research Center has been able to decipher that the true meaning to the words Good and Evil are "Function" and Dysfunction"
Logically the "fruits of the Knowledge of Good and Evil" is polar opposite from the "fruit of the Spirit"
but of the tree of the knowledge of good and evil you shall not eat, for in the day that you eat of it you shall surely die.” (Genesis 2:17 NKJV)
It is the Spirit who gives life; the flesh profits nothing. The words that I speak to you are spirit, and they are life. (John 6:63 NKJV)
This also points out that reliance on the "flesh" is comparative to the "fruits of the Knowledge of Good and Evil"
For he who sows to his flesh will of the flesh reap corruption, but he who sows to the Spirit will of the Spirit reap everlasting life. (Galatians 6:8 NKJV)
For only when one understands how the "fruits of the Knowledge of Good and Evil" cause death, can one understand how "Faith" repairs the damage It will be important to understand how "Faith" repairs the damage caused by the "fruits of the Knowledge of Good and Evil". For if by the "fruits of the Knowledge of Good and Evil" Adam and Eve were delivered into the fear of God. We will be able to understand what happens to this understanding when we apply "Faith". Yet if one does not understand the "fruits of the Knowledge of Good and Evil" and also does not understand how "Faith" repairs this problem.
Then the fear is not understood, and also the answer to communication with God, cannot be correctly given. So this is foundational, and does work towards the answer.
The "fruits of the Knowledge of Good and Evil" Eve considered 1. Pleasant to the eyes 2. Good for wisdom
So when the woman saw that the tree was good for food, that it was pleasant to the eyes, and a tree desirable to make one wise, she took of its fruit and ate. She also gave to her husband with her, and he ate. (Genesis 3:6 NKJV)
So it is pleasant to see the dysfunction of things, and also desirable because it makes wisdom. It is also pleasant to see the function of things, and also desirable because it makes wisdom.
An example of Eating of the Fruits
Imagine a hot day outside, and the air-conditioner breaks. Attention gets drawn to the dysfunction of the air-conditioner. Then occurs "Unbelief" that the dysfunction occurred. Like the statement "I can't believe that the air-conditioner has broken." With the unbelief then the attitude falls to anger, anxiety, or depression.
How then is the attitude maintained?
Faith that Love will correct the dysfunction.
This points out the difference between acknowledging the fruits of dysfunction, and eating those fruits.
One can be aware that the dysfunction has occurred, but it when it is allowed to affect ones attitude then the fruit has been eaten.
A proof from the perspective of the Law
If indeed the Law is necessary then why in the beginning was this single command given to Adam and Eve? For the nature of this understanding is the very proof that God found acceptable this environment. Now if God finds a situation acceptable, then there is no need to fear. As a comparative we can see the book of Romans.
For rulers are not a terror to good works, but to evil. Do you want to be unafraid of the authority? Do what is good, and you will have praise from the same. 4 For he is God’s minister to you for good. But if you do evil, be afraid; for he does not bear the sword in vain; for he is God’s minister, an avenger to execute wrath on him who practices evil. (Romans 13:3-4 NKJV)
For what is true for God's minister is also true with God. Why did they fear? Because eating of the fruit was evil.
Then let us understand the Catholic Faith
Now faith is the substance of things hoped for, the evidence of things not seen. (Hebrews 11:1 NKJV)
Let us apply it to our Air-Conditioner Parable
Imagine a hot day outside, and the air-conditioner breaks. Attention gets drawn to the dysfunction of the air-conditioner. Then the hope of a new Air-Condition, preserves the attitude, preventing the fall to anger, anxiety, and depression.
Therefore unbelief is the sign that the "fruits of the Knowledge of Good and Evil" have been eaten
And Faith is the acknowledgement of that dysfunction and hope that God can repair it.
Why is the spirit of a person so important to God?
God is Spirit, and those who worship Him must worship in spirit and truth.” (John 4:24 NKJV)
Must. And why? Because of the fear!
For God has not given us a spirit of fear, but of power and of love and of a sound mind. (2 Timothy 1:7 NKJV)
Seeing then that we have a great High Priest who has passed through the heavens, Jesus the Son of God, let us hold fast our confession. 15 For we do not have a High Priest who cannot sympathize with our weaknesses, but was in all points tempted as we are, yet without sin. 16 Let us therefore come boldly to the throne of grace, that we may obtain mercy and find grace to help in time of need. (Hebrews 4:14-16 NKJV)
Finding grace to help in time of need!!!!!!!!!!!!!! God is so awesome!!!!!!!!!!!!! When that dysfunction occurs, God wants to help fix it!
One who has "Faith" has stopped eating of the "fruits of the Knowledge of Good and Evil".
Therefore bear fruits worthy of repentance, 9 and do not think to say to yourselves, ‘We have Abraham as our father.’ For I say to you that God is able to raise up children to Abraham from these stones. 10 And even now the ax is laid to the root of the trees. Therefore every tree which does not bear good fruit is cut down and thrown into the fire. (Matthew 3:8-10 NKJV)
Being Heard through the "Righteousness of Faith"
Confess your trespasses to one another, and pray for one another, that you may be healed. The effective, fervent prayer of a righteous man avails much. (James 5:16 NKJV)
Why not the sinners?
Now we know that God does not hear sinners; but if anyone is a worshiper of God and does His will, He hears him. (John 9:31 NKJV)
Therefore by the deeds of the law no flesh will be justified in His sight, for by the law is the knowledge of sin. (Romans 3:20 NKJV)
But to those who are self-seeking and do not obey the truth, but obey unrighteousness—indignation and wrath, 9 tribulation and anguish, on every soul of man who does evil, of the Jew first and also of the Greek; 10 but glory, honor, and peace to everyone who works what is good, to the Jew first and also to the Greek. 11 For there is no partiality with God. (Romans 2:8-11 NKJV)
Because of God's Anger
Beloved, do not avenge yourselves, but rather give place to wrath; for it is written, “Vengeance is Mine, I will repay,” says the Lord. (Romans 12:19 NKJV)
God is a just judge, And God is angry with the wicked every day. (Psalm 7:11 NKJV)
So to Answer the question
Jesus is telling the general public (who has repented) to speak directly to the Father. Only those who have "Faith" particular the "Catholic Faith" will be heard. For every other denomination put their faith in Jesus dying for them. And indeed Jesus did die for them. And even Died for the forgiveness of sins. It is however not solely the belief that Christ raised from the dead or that there is a God that saves. God demands so much more then that.
Truly, these times of ignorance God overlooked, but now commands all men everywhere to repent, 31 because He has appointed a day on which He will judge the world in righteousness by the Man whom He has ordained. He has given assurance of this to all by raising Him from the dead.” (Acts 17:30-31 NKJV)
In fact as a message to those that believe and rely on his death
"But when the tenants saw the son, they said to each other, 'This is the heir. Come, let's kill him and take his inheritance.' 39 So they took him and cast him out of the vineyard and killed him. 40 "Therefore, when the owner of the vineyard comes, what will he do to those tenants?" 41 They said to Him, "He will destroy those wicked men miserably, and lease his vineyard to other vinedressers who will render to him the fruits in their seasons." (Matthew 21:38-41 NKJV)
For those without the "Catholic Faith" cannot even speak to the Father because it is foolishness to them.
But the natural man does not receive the things of the Spirit of God, for they are foolishness to him; nor can he know them, because they are spiritually discerned. (1 Corinthians 2:14 NKJV)
And it impossible for them to see it, or understand it
so that ‘Seeing they may see and not perceive, And hearing they may hear and not understand; Lest they should turn, And their sins be forgiven them.’” (Mark 4:12 NKJV)
For even believers do not know what to pray for
Likewise the Spirit also helps in our weaknesses. For we do not know what we should pray for as we ought, but the Spirit Himself makes intercession for us with groanings which cannot be uttered. (Romans 8:26 NKJV)
The only prayer that is heard anymore, is the prayer from the Spirit. Those with the spirit will be heard, those without the spirit will not be heard. Also Vise Verse
praying always with all prayer and supplication in the Spirit, being watchful to this end with all perseverance and supplication for all the saints (Ephesians 6:18 NKJV)
We are of God. He who knows God hears us; he who is not of God does not hear us. By this we know the spirit of truth and the spirit of error. (1 John 4:6 NKJV)
An Example Prayer in the Spirit
Again let us say that the Air-Conditioner breaks. "Can we get a new Air-Conditioner?"
An Example Prayer that does not Work
Again let us say that the Air-Conditioner breaks. "How many times do I have to tell you to never touch that Air Conditioner! Can't you just die already!"