Why we need to repent our sins

Question:
Why do we need to repent our sins if we are justified by faith (See Rom. 5:1), and only need to believe in Jesus Christ to obtain eternal life (See Jn. 3:18)?

Some might say we must repent our sins in order to validate one’s self as a believer. However, the example Christ gave us for validating one’s faith in him pertains to performing works of mercy, illustrated by his parable of separating the sheep from the goats (Mt. 25:31-46). Those who gave food, drink, clothed, etc., to the least of his brothers are invited to enter the kingdom of God because they did those things unto him, and those who did not do those things neglected him and are denied entrance into the kingdom. If repentance were the means for substantiating one’s faith in him his parable would have at least mentioned the need for our repentance; of which there is none.

Consider this; if repentance of our sins was necessary for one to receive eternal life wouldn’t that compromise the belief that we are justified by faith? It would seem that such a condition believes the work of redemption accomplished by Jesus was incomplete because having faith isn’t enough to obtain forgiveness for our sins. The Church has always maintained all the way back to the apostles that the work of forgiveness for our sins was accomplished completely by Christ’s sacrifice on the cross; yet the Church, also back to the apostles, consistently preaches the need for repentance of sins.

Consider as well Paul’s dialogue in Romans, chapters 3 - 8. He goes to great length to try and explain; though we are justified by faith we cannot just continue sinning (Rom. 6:1-4). Why would Paul experience the need to exert so much effort to teach the need to avoid sin if his teaching about salvation, which gives all the credit for our justification and salvation to the work accomplished by Jesus’ sacrifice on the cross, wasn’t misinterpreted by the people of his time as giving them the freedom to sin? A misunderstanding many people still make even to this day.

And so I pose the question: Why did the Lord command us to repent our sins?

Visit: "A Layman's Journey: In Search of Spirituality" for my view.