It is the "first word of the gospel". John the Baptizer preached it, Paul preached it, Peter preached it as being necessary.
Jesus's own words were "Repent or you will perish."
I'd say that it must be absolutely necessary.
It is a change of the mind. It is a change of the will. It is a change of the heart. It is a change of allegiance. It is a change of ownership (from Satan to Jesus) It is part of the complete transformation called sanctification that the Holy Spirit begins when we yield ourselves to Christ. Jesus cannot or, at least, He will not really transform you against your will. He might need to do an attitude adjustment first so that you will yield.
Will we be perfect? no. Will we "continue to sin"? yes! unfortunately, we will. "If one says they have no sin, they are a liar and the truth is not in them." But, we can longer willfully sin without consequences.
We cannot be saved unless Jesus is our Savior. We cannot repent without believing. We cannot confess Jesus as Lord without repenting. Jesus will not be our Savior unless He is also our Lord. We cannot be saved unless we repent. So, the necessary ingredients of salvation are: We must believe (trust in Christ as Savior, not mere head knowledge.) We must repent of our sins and "change directions on the Roads of Life." We must confess Jesus as Lord.
Salvation is like a 3-legged table. The 3 legs are Faith, repentance, and Lordship. It won't stand without all 3.
