Spoken like a Pharisee... It is amazing how many people do not read 1 John.
Let's just go ahead and establish that you are perfect and righteous. You have never committed a sin since you repented. and therefore you have never had any reason to pray: "forgive us our trespasses". twice.
That being said, the rest of us are not perfect but are being moved towards perfection. While we have the Spirit of God, we still inhabit the flesh of this world, and therefore are still susceptible to stumbling in the face of strong temptations.
Temptations like lust, anger, greed, etc. You don't have to steal to be a thief. You don't have to kill to be a murderer. Or an adulterer to commit adultery.
We stumble and fall, and we repent and pray to never commit that sin again. But being human, There is a strong possibility that we will sin again. and so we repent again. Striving always to be sinless.
1 John 2:1-2
Do not sin, but if you do, ask for forgiveness and you will be forgiven. We are saved by mercy and grace, not by legalism. If it were possible for us to live a life without sin in these bodies, there would be no reason for church or anything. The Holy Spirit puts into us a new heart. A heart with the law written on it. And he gives us strength to follow that law, but we are still fallible.