It would be fair to say, one of the trickier things to understand in the Bible is the harmony between the plurality of God and the singularity of God. We know that God is one (Mk 12:29). Likewise, we know that God is comprised of three persons (1 Pet 1:2) - God the Father, the Spirit (Holy Spirit, Holy Ghost), and Jesus Christ (the Son). The difficulty with the Godhead (as we informally refer to Him) is not identifying His person but differentiating between the three comprised persons. We know they possess equality in rank (Phil 2:6) but sometimes can be confused regarding their differences in role.
Each person of the Godhead performs a particular function(s) in the life of a Christian. Christ is no exception to this. Nevertheless, Christ, being equal with God (Jn 1:1, 14; Jn 17:21), is still distinct from both the Father and the Spirit. This distinctive nature is demonstrated in His role as it relates to sanctification, advocation, and mediation for the Christian.
First, Let's address Jesus' role in sanctification. Before Christ, the Godhead had two separate forms of religion. The first was Patriarchy, which involved the household's father serving as a priest and demanding godliness or moral excellency (example - Job). This covenant existed with the Gentiles (Rom 2:14-16). The second was the Law, or Judaism (often referred to as The Law of Moses). This was established as Mount Sinai (Ex 19), and it was required exclusively of the Jews. Both of these forms of religion were good, yet they possessed some insufficiencies concerning the constant need for sacrifice (Heb 10:4, 11). These two forms of religion were done away with at the purchase of the church (Acts 20:28; Col 2:14) and its establishment (Eph 2:13-22). Now, Jews and Gentiles were reconciled to one religion, Christianity. In Christianity, sanctification was complete. Jesus provided a sufficient sacrifice (1 Pet 1:18-19), one that eliminated sins (Eph 1:7), all sins of all people (1 Jn 2:2), and did so in such a perfect way that it would only be required once (Heb 10:12-14). Jesus is the perfecter of our sanctification.
Second, Let's address Jesus' role in advocation. As aforementioned, there were two separate religious forms, Patriarchy and Judaism. Each of these systems had its own laws for dealing with sins. Each person, under both, had a personal responsibility to deal with sin but also appointed figures to be the spiritual leader or advocate for sins. Under the Patriarchy, you had the head of the house filling this role, and under Judaism, you had the high priest serving in this role. Both would intercede on behalf of the sinner. Here is where the insufficiency lies. Proper advocacy would require equality of the advocate with both parties being reconciled. Clearly, under these two religious forms, this was an issue. Yes, the men could advocate well on behalf of sinful men. They knew perfectly what it meant to be them and experience their struggles. However, the men could not advocate well on behalf of God; He is perfect and free from sin, an experience they could not share. This is where the majesty of Christ is displayed. He knew perfectly what it was like to be like God, sinless (2 Cor 5:21; 1 Pet 2:22). Likewise, He understood perfectly what it was like to be like man, tempted (Heb 2:14, 18). This is what made Him perfect for advocacy. He knew what it was like to be tempted, yet He resisted those temptations and maintained His God-status through His perfection (Heb 2:17, 4:14-15). Now, instead of incomplete advocacy, we have complete advocacy. We have God the Son, who has shared our experience, pleading our case to God the Father, who has only experienced it from afar. Jesus makes everything so perfectly complete, even our case with the Father.
Third, Let's address Jesus' role in mediation. This naturally builds upon the previous point, advocation. However, this further addresses how Jesus performs advocacy through our prayers. Paul reminded us of only one mediator between God and man, the man Christ Jesus (1 Tim 2:5). He told us this in the context of prayer. This gives us insight into Jesus' function in our prayers. Previous to Jesus, men tried to intercede (mediate on behalf of another) for others on many occasions. Namely, we have the example of Moses interceding for the Hebrew people during their shortcomings (Ex 32:30-33). First, I will say, yes, this intercession worked. Second I will say, no, it was not to its completest form. We can say this because Moses struggled with sin. That is a problem that is non-existent with Jesus. With Jesus, we have perfect mediation. We have a perfect God-man delivering the earnest desires of our hearts, pleadings for mercy, and requests for strength and knowledge, all directly to the throne of God. In fact, with Jesus as our mediator, it tells us that we are brought directly to God's throne (Heb 4:16). That is a huge difference! It doesn't portray Christ as taking our prayers and coming to the Father, saying, "here is the request of one of your people." Instead, it depicts Christ as bringing us with Him to the Father and saying, "Here is one of your people. Let me share their requests, concerns, pains, and joys with you." This is prayer on a whole new level of intimacy. This is prayer made possible through the role of Jesus in mediation.
Thank the Father for His Son. He has blessed us so richly in giving His only Son. Not only do we get to know God more through Him, Jesus. But additionally, we get to reap the benefits of perfected sanctification, personal advocation, and privileged mediation. "Thanks be to God for His inexpressible gift!" (2 Cor 9:15).