All mankind is alienated from God because of sin. Men may think they are fulfilled when their fleshly desires are being satisfied, but sooner or later they will discover a feeling of emptiness in their inner life. God is not satisfied for man to remain alienated from him for in such a state God is unable to enjoy communion with him for God is altogether holy and cannot be associated with sin. Therefore, God took the initiative to bring about reconciliation of men with himself. This could be done only through a mediator. Concerning this I Timothy 2:5 ,6 says, "For there is one God, and one mediator between God and men, the man Christ Jesus: who gave himself for ransom for all, to be testified in due time (to be proclaimed as such in due time).
To become our mediator Jesus had to offer himself as the ransom price for our redemption from sin. Since the penalty of sin is death, our blessed Savior suffered the penalty rightly belonging to us that God might be just while justifying us. Romans 3:26. After having made atonement for our sins by shedding his own blood on the cross, he conquered death and ascended to the right hand of the father in heaven to become our mediator, or intercessor. "Wherefore he is able to save them to the uttermost that come unto God by him, seeing he ever liveth to make intercession for them." Hebrews 7:25.
I John 2:1 says, "If any man sin, we have an advocate with the father, Jesus Christ the righteous." He pleads on our behalf to the father not to withdraw his love form us but to forgive us for his sake (because of our faith in him).
Isaiah was inspired to say (in the past tense) 700 years before Christ's birth, "He hath poured out his soul unto death; and he was numbered with the transgressors; and he bore the sins of many, and made intercession for the transgressors." Isaiah 53:12. Jesus interceded for everyone in dying for them, but he personally prayed for his executors while on the cross. Luke 23:34.
Jesus is not only our savior, mediator and advocate personally, he is also the mediator of the new covenant between man and God. Hebrews 9:15.
It is a grand and gratifying thought that our God loved and cared enough about our well being in this life and eternally to provide such a one as his son to redeem us from sin and plead our case for us. However, he becomes all the above named things unto us only as we commit our life unto him in faith, obedience and loving service.