Who may come into God's presence and worship?
David asked the question this way: who may ascend the hill of the Lord or who may stand in his holy place? He alluded to the tabernacle. David brought the ark to Jerusalem and made a tent for it there on a hill. (2 Samuel 6). To go to the tabernacle, you had to ascend the hill of the Lord. To stand in the holy place, in the tabernacle, you had to be clean. He specifically addressed clean hands, a pure heart, and a soul not given to idol worship.
"Hands", "head" and "heart" represent of other things. “Clean hands" does not refer to washing, but to actions that are right. If you steal something, you do not have clean hands. You have dirty hands. But if you have not done wrong, you have clean hands.
A "pure heart" does not mean one with no plaque in the arteries, but a person of pure motives. In Matthew 5:8, Jesus said "blessed are the pure in heart for they will see God". This means you come to truly worship, not to be respected or to look good or to socialize with your friends or to make business connections or to look for clients. Thus, the one who could come to the tabernacle was one who had not acted sinfully, one who had not come out of improper motives.
Finally, one could not worship idols and come into God’s house and worship. God commanded that only he be worshipped. This was the very first commandment of the covenant law.
We can see that the one God allowed to come into his presence in the tabernacle had to be holy. This makes sense because we know God is holy and cannot tolerate sin in his presence. That is Isaiah's vision of Christ in Isaiah 6. God said “I am the LORD your God; consecrate yourselves and be holy, because I am holy. (Leviticus 11:44) Peter gave the same instruction to the New Testament Church, referring to this verse and writing “"Be holy, because I am holy." (1Peter 1:16)