Jesus' Coming is to be a glorious event. But it has its sobering side, too. There will be the separation of the sheep and the goats. Repentance is our way to remain sheep.
It's not enough to say we're turning away from sins; we must do that, time and time again. We are living in the end times and have since the Ascension, of which the first Christians were constantly aware. For us to be triumphant in Glory we must needs be triumphant in the things in our lives now. Too often we today are concerned with "being in fashion" and the repentant Christian, in this secular world, just isn't.
It is easy to say "I'm sorry" and then continue to do what is hurtful to ourselves and others. The hard part is stopping indefinitely. In fact, it's impossible for us to do alone. Only with the Holy Spirit can true repentance come. Today the Holy Spirit can help us truly repent of our sins and it's always today.