Becoming a Believer
God is holy and just, perfect in all things. When all men in Adam separated themselves from perfect relationship with Him by sinning, there was no way to restore that relationship through man's effort. Man is born a sinner, and is by nature and choice an enemy of God. Everything man does is corrupted by sin. Our self efforts at being righteous are unacceptable to God. His wrath against sin is completely justified and deserved.
He did not leave man without hope of being able to have a relationship with Him. God the Son became man--Jesus. Jesus was conceived miraculously through the Holy Spirit and was in nature and choice sinless. He lived a perfect life, then was condemned to die unjustly and cruelly on the cross. When He died, He bore the sin of man, satisfying God's demands for a perfect sacrifice in order to redeem and save a people unto Himself. He rose from the dead, conquering sin's death penalty.
This substitutionary sacrifice is available to all. Jesus said, "I am the way, the truth, and the life. No one comes to the Father, except through me." (John 14:6, ESV). It is not through self-effort that we have a relationship with God; it is through Jesus Christ's death on the cross that we are able to have forgiveness of sins and the hope of eternal life.
The answer is Jesus. "But now the righteousness of God has been manifested apart from the law, although the Law and the Prophets bear witness to it— the righteousness of God through faith in Jesus Christ for all who believe. For there is no distinction: for all have sinned and fall short of the glory of God, and are justified by his grace as a gift, through the redemption that is in Christ Jesus, whom God put forward as a propitiation by his blood, to be received by faith. This was to show God's righteousness, because in his divine forbearance he had passed over former sins. It was to show his righteousness at the present time, so that he might be just and the justifier of the one who has faith in Jesus." (Romans 3:21-26, ESV)