"If we claim to be without sin, we deceive ourselves and the truth is not in us." NIV translation
We all need a Savior each and every day. No matter what we may think of ourselves, each of us sins against God every day. If we cannot admit that, the "truth is not in us".
"If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness." NIV translation
One of the Hebrew names that describes God is El Hanne'eman and it reminds us that God is faithful. He will never forsake us or forget us and He keeps His promises. This verse is also a promise from God. If we confess and not try to deny or hide our sins, He will forgive and cleanse us. We can look at how God has kept His promises throughout the Bible and take comfort in the fact that El Hanne'eman keeps ALL of His promises.
"If we claim we have not sinned, we make him out to be a liar and his word has no place in our lives." NIV translation
This last verse may sound kind of harsh but, if we stop and meditate on it, it is absolutely true. If we, in fact, say that we have not sinned, then, there is no place for any part of the Word in our lives as the rest of the word speaks of salvation from sin. Jesus said that all have sinned. Therefore, if we say we haven't, we are in fact calling Him a liar and why would you listen to the words of a liar? But, if we all compare our lives to God's Law (the Ten Commandments), we can objectively see that we have sinned and therefore must have salvation and Jesus was right.