What a difference a word makes!

In the beginning of the book of Leviticus—before God had given his instruction through Moses to the people of Israel regarding their state of cleanliness in his presence—Yahweh (the LORD) spoke to Moses from the tent of meeting.

Why, from?

Because Moses could not enter; this was before the instruction had been given.

Then we continue reading and God (through Moses) gives to the Israelites everything they need to do to be clean before God. The rituals are extensive and somewhat boring and out-of-touch to us, but they meant everything for the Israelites. You see, there was a problem between them and God.