Ex 19:11

19:11 be ready for the third day. Arrangements to ensure ritual purity (washing clothes, v. 10; abstention from sexual intercourse, v. 15; Lev. 15:18; 1 Sam. 21:4) and to safeguard the holiness of the mountain (vv. 12, 13) were commanded in preparation for the theophany, a special visual manifestation of divine presence.

come down on Mount Sinai. The mountain was the Lord’s place of meeting with His people, not His residence. The tabernacle was soon to be His earthly dwelling place.