This applies to our poor miserable life. Although we believe God's Word, do His will, and are supported by His gifts and blessings, our life is still not sinless. We still stumble daily and transgress because we live in the world among people. They do us much harm and give us reasons for impatience, anger, revenge, and such. It is not possible to stand firm at all times in such a constant conflict.
There is a great need for us to pray, "Dear Father, forgive us our trespasses." It is not as through He did not forgive sin without and even before our prayer. (He has given us the Gospel, in which is pure forgiveness before we prayed or every thought about it.) But the purpose of this prayer is that we may recognize and receive such forgiveness. The flesh in which we daily live is ever active in evil lusts and devices, so that we sin daily. By this the conscience is thrown into unrest, so that it is afraid of God's wrath and displeasure. So it loses the comfort and confidence derived from the Gospel. Therefore, it is always necessary that we receive consolation to comfort the conscience again.
This serves God's purpose of breaking our pride and keeping us humble. God has reserved this right for Himself: if anyone wants to boast of his godliness and despise others, that person is to think about himself and place this prayer before his eyes. He is no better than others. (pars. 85-86,88-90)
Condensed from CONCORDIA: THE LUTHERAN CONFESSIONS, copyright 2005,2006 by Concordia Publishing House. Used by permission. All rights reserved. To purchase a copy of CONCORDIA, call 800-325-3040.