Moses, after he received the ten commandments and brought them down, went back up to the mountain and received further commands and orders from the Lord.
As God was giving him these further instructions on how to live in the light of His commandments, specific instructions about access to God, about how to come to God through the Tabernacle, through the priesthood, the offerings, and the furniture in the Tabernacle, the purpose was not just ‘how people could come to God’ but ‘how God could come to the people’.
Because God has a problem with us. That is: God is holy and we’re not holy. How then can a holy God come into fellowship with the people who are unholy and unclean in His sight?