Psalm 15 is a song of David from the ‘first’ book of the psalms (originally, the Psalms were not considered one document. They were combined into one document and numbered for the sake of ease in complete Bible printings). It is a song to God listing the character attributes of a man that will dwell with God and one who will not.
It has a great deal of truth concerning God’s character and what God considers to be good, but the passage is about men. Apparently neither David nor the Holy Spirit got the memo that man-oriented songs to God weren’t acceptable. With that, here’s the KJV text:
1Lord, who shall abide in thy tabernacle? who shall dwell in thy holy hill?
2He that walketh uprightly, and worketh righteousness, and speaketh the truth in his heart.
3He that backbiteth not with his tongue, nor doeth evil to his neighbour, nor taketh up a reproach against his neighbour.
4In whose eyes a vile person is contemned; but he honoureth them that fear the LORD. He that sweareth to his own hurt, and changeth not.
5He that putteth not out his money to usury, nor taketh reward against the innocent. He that doeth these things shall never be moved.
The overall message: do the right thing. Love God, hate evil, stay on the straight and narrow even if it hurts. It’s not complicated stuff, but not easy stuff either. Speak the truth in your heart? It’s hard enough to speak the truth with your mouth, even if it hurts (v5), but don’t even speak a lie in your heart? That’s tough.
What’s interesting to me is that the Bible clearly teaches conditional ‘election’ and commanded perseverance here, not the “unconditional election” and “once saved always saved” of many Protestants. Verse one asks a question about the future. The rest of the passage (aside from the last sentence) speaks for the present. You have a future with God if and only if you make the choice to do the right thing. Your individual “election” is conditional on your thoughts and deeds. If you sin, God offers forgiveness after repentance, but only after repentance (Ezekiel 18:27-28). This did not change after the resurrection of Jesus (Acts 26:18). Stop sinning
Verse 5 is a refutation of once saved always saved (also called perseverance of the saints or eternal security). Your salvation is maintained if and only if you do these things and do them with the right heart. You shall “never be moved” if you “doeth these things,” not, you will “doeth these things” because “you shall never be moved.” To believe the latter makes Ezekiel 18:27-28 and Acts 16:18 lies.
For those who will claim “imputed righteousness,” tread carefully. In order for forgiveness of sins to come only after repentance, if imputed righteousness is true, and you sin after being saved, either (1) there is sin with you after you have put on Christ, which puts sin with Christ or (2) God is unable to search your heart and know your thoughts and deeds after you are saved. So you have to choose between a God who’s a sinner and a God who is less than a puppet master. Either is blasphemous.