The Apostle John wrote his Gospel to declare that Jesus is the Son of God (Jn. 1:34). In fact, as the Son of God, Jesus actually IS God (Jn. 1:1, 14). Even His enemies recognized Jesus was claiming to be God. John wrote: "Therefore the Jews sought the more to kill Him, because He not only had broken the Sabbath, but said also that God was His Father, making Himself equal with God" (Jn. 5:18).
John's declares the reason God sent Jesus: "That whosoever believeth in Him should not perish, but have eternal life. For God so loved the world, that He gave His only begotten Son, that whosoever believeth in Him should not perish, but have everlasting life. For God sent not His Son into the world to condemn the world; but that the world through Him might be saved" (Jn. 3:15-17).
In order for us to be cleansed from our sin, and be made the righteousness of Christ, God sacrificed Jesus to save us. The Apostle Paul wrote, "For He hath made Him to be sin for us, who knew no sin; that we might be made the righteousness of God in Him" (2 Cor. 5:21). Jesus became our Passover Lamb, so that we might be saved by trusting in Him (Jn. 1:29; 1 Cor. 5:7)!
So, how does one become a born again child of God? You have heard the saying, "If it sounds too good to be true, it probably is." Well, this is the greatest exception to that. Read what Paul says in Romans 10:
 For they (the religious) being ignorant of God's righteousness, and going about to establish their own righteousness, have not submitted themselves unto the righteousness of God.  For Christ is the end of the law for righteousness to every one that believeth.  But what saith it? The Word is nigh thee, even in thy mouth, and in thy heart: that is, the Word of faith, which we preach;  That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised Him from the dead, thou shalt be saved.  For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.  For whosoever shall call upon the name of the Lord shall be saved."