Many, I suspect, feel this way because of self-loathing. Because their past sins haunt them, they "will" not to receive God's forgiveness. Some might even see their attitude as extreme humility, but what it really is, is a lack of faith...
And some, I suspect, are uncomfortable with unmerited grace and feel they must do something to earn it. They might see this as humility or gratitude instead of the insult to the Blood of the Lamb that it is...
And some, I suspect, believe the Blood of Christ fades over time - that when they sin again, the forgiveness they once received is cancelled...
EXCELLENT summary of the many spiritual ills which keep us from understanding that Christ is our "all in all."
What fruit had ye then in those things whereof ye are now ashamed? for the end of those things is death. But now being made free from sin, and become servants to God, ye have your fruit unto holiness, and the end everlasting life. " -- Romans 6:14,21-22"For sin shall not have dominion over you: for ye are not under the law, but under grace...
Praise God! What an extraordinary, free, unmerited, merciful gift has been given to those He has "planted together" (Romans 6:5); those who were once "servants of sin" but who now have been "made free from sin" and reborn as "servants to God."
"the gift of God is eternal life through Jesus Christ our Lord." -- Romans 6:23
And if Christ [be] in you, the body [is] dead because of sin; but the Spirit [is] life because of righteousness. - Romans 8:9-10
I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me. - Galatians 2:19-20
To God be the glory!