This is a faithful saying and worthy of all acceptance, that Christ Jesus came into the world to save sinners, of whom I am chief. However, for this reason I obtained mercy, that in me first Jesus Christ might show all longsuffering, as a pattern to those who are going to believe on Him for everlasting life. (1 Timothy 1:15-16)
People can feel so guilt-ridden by their past that they think God could never forgive and accept them. But consider Paul's past. He had scoffed at the teachings of Jesus ("a blasphemer") and hunted down and murdered God's people ("a persecutor and a violent man") before coming to faith in Christ (Acts 9:1-9). God forgave Paul and used Paul mightily for His kingdom. No matter how shameful your past, God also can forgive and use you.