When I put on my anti-wrinkle cream at night, I'm trying to turn back the hands of time and "undo" what nature has already done. Unlike my magical, always-stay-young-cream, Jesus doesn't turn back the clock on our life when we're saved by grace through faith. He doesn't change what we've done, but He DOES take away the guilt. When our guilt is gone, we have peace. If we don't have peace, one of two things may be holding us back--unbelief or Satan.
If it is unbelief, we remain miserable and ineffective until we begin to believe God's words in Isaiah 43:25, "I am the one who wipes out your transgressions for My own sake, and I will not remember your sins." How plain can God put it? Until we decide in faith to believe God, we're stuck in sin. Romans 14:23 says, "Whatever is not from faith is sin."
The other reason we feel guilt is because Satan heaps it on us. If he can keep us feeling guilty, he'll flatten us with it. Satan means "accuser". He'll get us any way he can. But don't make him your focus. Don't live in fear of Satan's attacks. Simply be aware of how he operates and his schemes to get you.
If we can learn to live in the light of God's truth, we can handle each of Satan's attacks and have victory over each one.