So the angel said to those standing before him, “Take off his filthy clothes!” Then he said to Joshua, “See, I have removed your iniquity, and I will clothe you with splendid robes.” — Zechariah 3:4

David resolved to set the Lord always before him. That's a deliberate act of the will — not a feeling, a choice. Because the Lord is at your right hand, you shall not be shaken. This is what it means to walk by faith, not by sight, and to fix your eyes on what is unseen. When everything around you is shifting, setting the Lord before you keeps your footing firm.