Good morning! This was written as a spiritual father to those he raised in the Gospel to instruct them so they do not sin. He doesn't do this with the thought we will never fall short.
Humans have moments of weakness, mistakes, and even carnality. It doesn't mean because we have these tendencies we should give up trying to stay sinless. We should strive to walk in step with the Holy spirit.
When we do slip, we have Jesus who made intercession for us through His blood to help us in our weakness, cleanse us from unrighteousness and set us back on the path of our salvation. Rely on the Holy Spirit to guide and direct you as you live this life of faith. Jesus makes it possible to stay in constant fellowship as you make a great day!