Albert Barnes Commentary Exodus 33:5

"And Jehovah said unto Moses, Say unto the children of Israel, Ye are a stiffnecked people; if I go up into the midst of thee for one moment, I shall consume thee: therefore now put off thy ornaments from thee, that I may know what to do unto thee." — Exodus 33:5 (ASV)

I will come up ... - Better: If I were to go up for one moment in your midst, I would consume you.

That I may know ... - By that sign of their repentance Yahweh would decide in what way they were to be punished.