 | If I had cherished sin in my heart, the Lord would not have listened; but God has surely listened and heard my voice in prayer |
 | If I regard iniquity in my heart, the Lord will not hear me: But verily God hath heard me; he hath attended to the voice of my prayer. |
Ongoing sin in a believer's life hinders effective prayer (Ps. 32). This is especially true if we cherish certain unconfessed sins in our lives.
Proverbs 23:17 says "Do not let your heart envy sinners, but always be zealous for the fear of the LORD."
We are commanded not to cherish sin or envy sinners.