Well, I disagree, in a sense...The Bible never tells us to, "repent of our sins", to be saved. It does say to repent toward faith toward Jesus Christ, to change from unbelief to belief in him. And that particular kind of repentance is a one time act.
Testifying both to the Jews, and also to the Greeks, repentance toward God, and faith toward our Lord Jesus Christ...repentance from dead works, and of faith toward God, Acts 20:21, Hebrews 6:1b
After we are saved we repent daily of sinful attitudes, behaviour, etc. as the Spirit leads us, not to obtain or maintain salvation, but to grow in grace. Once we have believed, God treats us as his adopted sons and corrects those he loves--us. This is where repentance of sin comes in, not at all to add to what Christ did for our salvation, but to help us grow. When we did repent to faith toward Christ for salvation, we also changed our mind about sin as we admitted we were sinners in need of a Saviour and trusted Christ.
The formula is: trust Christ for salvation, obey him for growth, not, stop sinning, then trust Christ. After one trusts Christ, comes just as they are, one will develop a new attitude toward sin, although they will still sin. This is a process known as sanctification. When we trusted Christ, we were justified. Now that our sins were all (past, present and future) paid for by Christ, God looks at us "just-as-if-I'd" never sinned, and God looks not at our useless "dead works of righteousness", this so-called "repenting of our sins", but at Christ's work of righteousness for us. Sanctification is where daily repenting of sin occurs. While it is correct to say because of our belief in Christ we were sanctified, our spirit was made alive, separated to God, sanctification is also an ongoing process as our body and soul begin to be conformed to the image of Christ. This is where the "chastisement of sons", the correction and leading of the Holy Spirit comes in to help us grow in grace. "in grace" means we are saved, adopted children of God. Like a newborn baby, we are "in the family" forever. Now we are growing up! Those who mature fastest repent more.