The answer to this question is not so obvious and may seen contraindicative. The average Joe would think that the purpose of Christianity is to live by the Golden Rule or to love one's neighbor or be a good Samaritan or in some way just be a good person. Yes, God is love and he who loves another fulfills the Law of Christ who told us to love each other as He loved us.
But the point is that people of all faiths think they are "good," and that the purpose of all religions is to be good. Yes, if that is all you choose or want or aspire to be is good (in whose eyes though?) then ANY religion will do. There are good Jews, Mormons, JWs, Muslims, Hindus, and Buddhists, and you could even argue for good Secular Humanists or even in some cases, good atheists, which only proves you don't need religion to be good. This sense of good and evil comes from God who gave everyone a moral compass or conscience to judge right and wrong and holds us accountable.
Don't people realize that our righteousness and good deeds are as filthy rags in God's sight and count for nothing by way of salvation? When we say we are good, we contradict the Lord who said only God is good--we are then evil in comparison because God doesn't grade on a curve; however, people play, "Let's compare," and don't realize God is the standard, not our neighbor; in comparison to Adolf Hitler, I am a saint! People all commend themselves!
But God has leveled the playing field and labeled, reckoned, and judged us all sinners who fall short of God's glorious ideal and measure of perfection. Paul called himself the "chief of sinners" yet he is numbered among the saints!
Jesus made an important point to Peter when He asked the disciples: "Who do men say that I AM?" This is what Christ was trying to point out! Jesus also said, "Unless you believe that I AM, you shall die in your sins..." John 8:24 Jesus is God in the flesh! This means that we must correctly understand who Jesus is.
We must realize Christ as our Lord and Savior not just some moral guide, Exemplar, martyr for a noble or good cause, victim of an evil society, but as one who voluntarily laid down His divine life and even chose the moment to expire for us.
The whole point of Christianity is to know God and Jesus His Son. This is eternal life in essence and consists of a vital, growing, living, saving faith and relationship with the triune Godhead. John's Prologue says that the Word became flesh and dwelt among us! John 1:14 Yes, this is the point we must grasp to be saved. The point then is as the question goes, Do you know God? Not are you a good person. Jesus didn't come to make bad people good but to make dead people live!
All religions teach us to be good and people even know that much by their own conscience. Don’t forget true faith expresses itself and has fruit for we are to be a redeemed people zealous of good works, thus validating our faith in the eyes of men. Soli Deo Gloria!