What is it that only Christianity does for us that we can't do for ourselves, and that no other religion solves? All religions with a God (or gods) claim that their God is real (or their gods are real), so it can't be that. What is Christianity's unique claim, and how does it benefit us?
Christianity solves the problem of sin. God’s inspired and holy Word makes it clear that sin is what separates humans from God:
for all have sinned and fall short of the glory of God (Romans 3:23).
Therefore, just as sin came into the world through one man, and death through sin, and so death spread to all men because all sinned (Romans 5:12).
Many other religions deny that humans are sinful and that a loving God will simply forgive them if they strive to be “good” and follow a system of works that will appease God. They believe that they can reach up to God by their own efforts. Christianity, on the other hand, is the only religion where God reaches down to us. God knows that sinful, imperfect humans can never keep his perfect laws and that is why He sent His Son to pay the penalty for sin so that all who place their faith in him might be forgiven. By faith in Him and accepting His work on our behalf, we are justified and made righteous. Here is the crucial difference between Christianity and all other religions.
Unlike other religious systems that insist upon following all sorts of rules and regulations, Christianity is a relationship with God, one that He initiated and maintains. It is God who has provided the solution to sin, through the perfect life of Christ Jesus, who came to earth to do the will of his Father who sent him. By his death on the cross, Christ Jesus restored the relationship that was broken by sin. Having been purchased by his shed blood, all who believe in Him are saved from the penalty of sin and are adopted into God’s family:
he entered once for all into the holy places, not by means of the blood of goats and calves but by means of his own blood, thus securing an eternal redemption (Hebrews 9:12).
he predestined us for adoption to himself as sons through Jesus Christ, according to the purpose of his will (Ephesians 1:5).
This is unique to Christianity – that God so loved the world He sent His Son so that everyone who believes in him will be forgiven, justified and sanctified and have eternal life (John 3:15-16).
The resurrection of Christ Jesus is the evidence that Christianity solves the problem of sin. No other religion can claim that their deity, their prophet or their leader rose from the dead. Buddha did not rise from the dead. Muhammad did not rise from the dead. Confucius did not rise from the dead. Krishna did not rise from the dead. Only Jesus has physically risen from the dead, walked on water, claimed to be God, and raised others from the dead. He has conquered death. The resurrection of Christ Jesus is God’s guarantee to all who place their faith in Him of a future resurrection to eternal life. After His death and burial, Christ Jesus rose again, and now lives at the right hand of the Father, interceding for believers forever:
Consequently, he is able to save to the uttermost those who draw near to God through him, since he always lives to make intercession for them (Hebrews 7:25).
This is the unique claim of Christianity, that God has provided the solution to sin and that all who believe in His Son can enter into relationship with God:
Jesus said to him, “I am the way, and the truth, and the life. No one comes to the Father except through me (John 14:6).
Man, in his creativity, has invented innumerable religions in his attempt to reach God. God, in His love, has given us the truth: the one religion, Christianity, in which God attempts to reach man. Source: https://www.gotquestions.org/Christian-religion.html
My answer comes from a Reformed Protestant view.
There was once an Oxford university debate about what made Christianity unique among all the world's religions. The debating chamber was full and many speeches were made. Passing by, hearing the debate, C.S. Lewis enquired what it was all about. Upon hearing it was to know what made the Christian God unique, he said, "Oh, that's easy. It's the grace of God."
Uniquely, Christianity alone presents the wonder of the holy God being gracious towards sinners who will repent and trust in God's provision for salvation. The persons God is gracious towards cannot earn, or merit his favour, however. Grace is undeserved (otherwise, it would not be grace, but due recompense, or a wage earned.) Now, other religions may speak about grace and have a theology of divine grace, but Christianity alone has this God of grace "coming down to us", as it were, to lift us up to places of spiritual wellbeing (sometimes literal wellbeing, as with how he ensured Noah and his family survived the flood.)
Once a person has experienced the unmerited grace of God, they remain astounded that God took the initiative, saved them from due punishment for their sins, and then directed their lives. He not only took an interest in their salvation, but in them, as a person. I recommend the booklet below for a good explanation of this, from the Bible.
So, the problem to which Christianity has a solution is how a holy God could have any favourable dealings with unholy sinners. God solves the problem for us by taking the initiative in sending his sinless Son to identify with us to the extent that the Son becomes one of us, dying in our stead to bear the punishment we deserve, so that repentant believers can pass over from judgment to life at that point of faith, due to nothing they have done; it is all entirely of God, so nobody can boast, or claim they have added to God's plan of salvation, in order to complete it (Galatians 6:14; Ephesians 2:9). The plan was worked out in the Godhead before any creation was done (Ephesians 1:4; 2 Thessalonians 2:13), carried out at God's timing (Romans 5:6-8), in God's way (Isaiah 55:1-11), and now the finished work of Christ on the cross means we can experience the loving grace of God. We certainly could not ever do anything to secure any of that!
Alas, all man-made religions exhort people to do this, that, and the other, to climb their way 'up' (as it were) to heaven or nirvana; to do more good things than bad things so that they might tip God's scales in their favour and just hope that God will be more merciful than judgmental towards them. Whatever the variations on that theme, the common denominator is that nobody can be sure that God will let them 'pass' into heaven or on to a paradise earth, or wherever; they must vigilantly keep working on themselves and their deeds, striving ever harder. But Christianity first emphasizes the bad news — that no amount of things we do can ever help get us right with God — before sharing the good news — that Christ is the way to being made right with God, putting faith in what he did to redeem us. That's the problem, and the solution, uniquely expressed in Christianity alone.
I am answering from a Reformed Protestant standpoint.
Account about a statement from C.S. Lewis's - it will be in a book somewhere, but I don't have the source.
"Explaining The Grace of God", Charles Strohmer, Sovereign World, 1993 https://www.gotquestions.org/QOTW.htm Question of the Week: "Is Christianity a religion or a relationship?"
Christianity doesn’t solve any problem. Jesus does. However, I appreciate your intent with the Q, so lets look a little closer at the ‘problem’ that needed solving.
GEN 3:13 Then the Lord God said to the woman, “What is this you have done?” The woman said, “The serpent deceived me, and I ate.”
The problem was man became separated from God. His ‘spirit’ was separated when ‘he’ choose to become his own ‘source’ of righteousness. ‘He’ [man] would use his own ‘understanding’ of ‘right and wrong’ to be ‘right’.
But ‘man’ was not created to be able to ‘be righteous’. Impossible. Only God is righteous. (But) Man decided he would become like a god and be responsible for his ‘own’ righteousness, that is, self righteous.
Jesus came to give us, or rather provide a way for man to be able to once again have access to Gods righteousness. That righteousness man needs for ‘life’. (Eternal life). Only God's righteousness is righteous.
All other religions do not [can not] offer righteousness, they [try to] provide a path/incentive/way for man to ‘work/behave/achieve his own righteousness. The only man who ever came close to achieving this was John the Baptist.
MAT 11:11 Truly I tell you, among those born of women there has not risen anyone greater than John the Baptist; [snip]
So the ‘problem’ that is solved is providing a ‘source’ for righteousness.
MAT 5: .20 For I tell you that unless your righteousness surpasses that of the Pharisees and the teachers of the law, you will certainly not enter the kingdom of heaven.
This question seems to presume that all religions are equally valid, and that there should be rational or emotional reasons why we should individually choose one over the others.
It would be a good question, if we knew that all religions are equally false. In that case it wouldn't really matter which one we choose, or none at all. Whichever one works best for our individual needs is the right one. Religion would effectively be a social club. In fact, that is the way most people in the First World seem to view religion.
But suppose that there is one religion that actually is true. Then it would make no sense at all to choose any religion other than that one, regardless of whether it is in many ways "not as good" as some of the others.
In that case, and this being Christianity.SE, the obvious answer to this question is: Christianity is unique in being the only religion that is true.
Every other religion requires people to be good or/and do good to obtain some eternal benefit - new life that will not expire or/and is somehow of greater significance, power or has better benefits than this life.
Christianity offer similar benefits, but the doing/being good is accomplished on our behalf by Christ. He is the man God sent to 'be good' for us, so we don't have to.
Eternal life is a gift - we cannot earn it, work for it, be owed it or otherwise obtain it by our efforts or attempts to 'please God'. The bible informs us that every man is held under sin (Adam's original sin) and the power of death that sin holds. Jesus broke that cycle (by dying as a sinless man) and defeated death for all - ALL!
But so also the gift is not like the trespass. For if by the trespass of the one, the many died, how much more did the grace of God and the gift in grace, which is of the one man Jesus Christ, abound to the many! Rom 5:15
According to God's word the bible, there is a burden of death that must be borne for all sin - each can bear their own burden (or penalty), but they will stay dead and that's it - never to be seen or heard again.
Jesus paid the penalty for all because his sinless life, by the grace of God, covered all human sin. He was then raised to immortal life by his Father and God. Christian baptism symbolises the joining to Christ's death and new life.
Therefore we have been buried with Him through baptism into death, so that, just as Christ was raised from the dead through the glory of the Father, so we too may walk in newness of life. Rom 6:4
So the 'problem' Christianity solves is the hopeless state believers find themselves in of not being able to fix their sin and the resultant death penalty that hangs over us. Christ has fixed it for us - he asks us to believe in him and his Father's gift.
We cannot do this on our own either. God makes Himself known to each person at some time. If they have missed out so far, as perhaps billions have, they will get their opportunity to accept Christ's sacrifice at some later time - after a resurrection to physical life. It is God who calls each person (at the time of His choosing) to know that He is, and rewards those who seek Him. (you cannot 'seek' Him if you don't know who He is, so the first step is always His)
For God is working in you, giving you the desire and the power to do what pleases him. Phil 2:13
And without faith it is impossible to please God, because anyone who comes to him must believe that he exists and that he rewards those who earnestly seek him.
The associated ‘problem’Christianity solves is eternal life for all. Not by default, but by a fair and reasonable offer being made available to all to choose. If one does not believe in God, then God has not opened that person’s heart and mind to knowing the true God. How then can they have or make a choice? They cannot, but they will have their opportunity.
In just the same way your Father in heaven does not want any of these little ones to be lost. Matt 18:14
God our Saviour, who desires all men to be saved and to come to the knowledge of the truth. 1 Tim 2:4
If these simple, unequivocal truths don’t fit your theology, then the theology is needing some adjustment!
Edit based on posted comments. The cries of 'heresy' are plainly based on teachings not of the bible - the word of God. It seems some would rather believe popes and preachers than dig a little to find the truth about salvation for all men. While it seems to be that some will die an eternal death - it will not be by chance or 'flat tyres'! The provision of grace and the Messiah's sacrifice is sufficient to cover all sin and remove that penalty for all. All will have opportunity to avail themselves of it - should they choose to. The resurrections will see to that. Rom 5 covers this all encompassing provision.
we have heard for ourselves and know that this one truly is the Saviour of the world.” John 4:42
But we see Jesus, who was made a little lower than the angels, because of the suffering of death, having been crowned with glory and with honour, so that by the grace of God He might taste death for everyone. Heb 2:9
For as in Adam all die, so also in Christ all will be made alive. 1 Cor 15:22
And on this mountain He will destroy the covering which is over all peoples, The veil which is stretched over all nations. He will swallow up death for all time, Is 25:7
For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life. John 3:16
The various doctrines that serve to misguide and distract from the truth of God's love and provision are not of Him, but of men. This allegiance to denominations is a distraction and also not of God. We were warned.