The people are coming to the door of the temple. The worship leader has already begun to sing, and the people hear and repeat, even from outside. They sing, "Lord, who may abide in Your tabernacle? Who may dwell in Your holy hill?" What it means is "Who can come into this place; who can come before the infinite, almighty, holy Lord God?"
As the leader sings on, All the people are made aware of the only answer to that question. He sings, "He who walks uprightly, and works righteousness, and speaks the truth in his heart; he who does not backbite with his tongue, nor does evil to his neighbor, nor does he take up a reproach against his friend; in whose eyes a vile person is despised, but he honors those who fear the Lord; he who swears to his own hurt and does not change; he who does not put out his money at usury, nor does he take a bribe against the innocent." Of course each time the leader sings a few of these words the people repeat them, and then they can't but consider their own hearts to see if they meet the requirements.
It's a practical lesson in personal righteousness - righteousness which the Lord requires of any earthdweller who would presume to come into His presence - who would presume to be one of His special people. As they sang about Him Who sees and cares about even their most insignificant activities, their awe of such a holy God surely must have increased!
That's why the leader then sings, slowly, distinctly, and possibly almost in a whisper, "He who does these things shall never be moved." The people repeat it in reverence, and then every soul is silent, every heart in deep meditation on the question of whether he or she meets these requirements and can come before such a God.
It's a lesson for us as well. We should ask ourselves the question, "Am I aware that God sees absolutely everything that's in my life"? Have I been concerned enough for personal holiness while I live on His property? How indeed do I treat other people? God grant us to walk in carefulness before His Face all the day!