Although some religions teach otherwise, the Bible makes it very clear that there is only one mediator between sinners (aka: each and ever person who has ever and will ever live) and the holy and righteous God. It is because of our sin (which we are born in) that we need mediation. We cannot approach God in our sinful state.
That mediator is Jesus Christ. Jesus declared himself to be “the way, the truth and the life,” and said no one comes to God the Father through any other means.
We are separated, until Jesus makes a way. The only way is through faith in what he accomplished on the cross, where Jesus bore the punishment for our sins (Isaiah 53:5, Romans 3, 1 Peter 2 and more).
But even after we’ve been converted by faith, Jesus remains our mediator with God the Father throughout our Christian life. 1 Timothy chapter 2:1-7 makes this very clear as it talks about prayer:
First of all, then, I urge that supplications, prayers, intercessions, and thanksgivings be made for all people, for kings and all who are in high positions, that we may lead a peaceful and quiet life, godly and dignified in every way. This is good, and it is pleasing in the sight of God our Savior, who desires all people to be saved and to come to the knowledge of the truth. For there is one God, and there is one mediator between God and men, the man Christ Jesus, who gave himself as a ransom for all, which is the testimony given at the proper time. For this I was appointed a preacher and an apostle (I am telling the truth, I am not lying), a teacher of the Gentiles in faith and truth. (ESV) [Emphasis added]
Jesus’ blood washes away our sins, his righteousness is imputed to us (by grace, through faith) and even more incredible, Jesus remains our mediator forever — interceding for us at the right hand of God the Father. Romans 8 also speaks to this when Paul writes about those who are “in Christ Jesus.” This beautiful chapter that begins with the assurance that “there is no condemnation” for those who are in Christ, continues with other assurances before getting to this one:
What then shall we say to these things? If God is for us, who can be against us? He who did not spare his own Son but gave him up for us all, how will he not also with him graciously give us all things? Who shall bring any charge against God’s elect? It is God who justifies. Who is to condemn? Christ Jesus is the one who died—more than that, who was raised—who is at the right hand of God, who indeed is interceding for us. Who shall separate us from the love of Christ? Shall tribulation, or distress, or persecution, or famine, or nakedness, or danger, or sword? As it is written,
“For your sake we are being killed all the day long;
we are regarded as sheep to be slaughtered.”
No, in all these things we are more than conquerors through him who loved us. For I am sure that neither death nor life, nor angels nor rulers, nor things present nor things to come, nor powers, nor height nor depth, nor anything else in all creation, will be able to separate us from the love of God in Christ Jesus our Lord. (ESV) [Emphasis added]