The power of God is the preaching of the cross!
1 Corinthians 1:18 For the preaching of the cross is to them that perish foolishness; but unto us which are saved it is the power of God.
That's the gospel of Christ (1 Corinthians 15:1-4 KJV), the power of God unto salvation to every one that believeth (Romans 1:16-17 KJV.
You deny the power and Him by your so called works!
2 Timothy 3:5 Having a form of godliness, but denying the power thereof: from such turn away.
Titus 1:16 They profess that they know God; but in works they deny him, being abominable, and disobedient, and unto every good work reprobate.
We have to go to Jesus for the forgiveness of sins. We get forgiveness of sins by confessing and repenting of them.
Jesus forgave people before the cross, when he walked the earth, and while on the cross, and after the cross.