This is a "call to worship" song. Before Christ's death, only the High Priest could enter into the holiest place in the tabernacle/temple (the Holy of Holies) and go before God. Approaching the glory of all-holy God is deadly to unclean sinners, so the priests had to go through meticulous physical and symbolic cleansing ceremonies before going in.
The word "Sin" is not a very popular word these days - a little "politically incorrect". Sin is simply the act of rebelling against God. It is he act of deciding that what I want is more important than what God has commanded me to do or not to do. As much as we try to "be good" and try not to "be bad", we still live with our sinful nature. We still do and think what we try not to, and we still don't do all we should do.
Breaking or omitting even one of God's commandments makes us unworthy to stand before His holy righteousness and justice for anything other than a death sentence. God would not be absolutely fair and just if He simply overlooked our sinfulness. But God is also a God of perfect love and mercy.
Because of God's love for us, He has provided a payment through Christ to pay the "debt" of our sinfulness. Christ's righteousness has been imputed (an accounting term meaning "credited") to us. Our sin was imputed to Him, which He paid for with His death on the cross.
Christ's atoning work on the cross sanctifies His people so that we can come directly before God in prayer and worship. We now have the honor and privilege of entering into the presence of the Creator of the Universe. It is not out of a sense of duty that we strive to follow the path laid out for us by God. It is a response to what He has done for us in love.
Under the Law,
before Christ:
2
Chronicles 23:5-6: ...all the people shall be in the courts of the house
of the LORD. But let no one come into the house of the LORD except the priests
and those of the Levites who serve...
From King David's perspective:
Psalm
5:7: Because of Your unfailing love, I can enter Your house; with deepest
awe I will worship at Your temple.
From our perspective:
Luke
14:23: -Then the master said to the servant, "Go out into the highways
and hedges, and compel them to come in, that my house may be filled."