Charles Spurgeon Commentary Exodus 32:28-30

"And the sons of Levi did according to the word of Moses: and there fell of the people that day about three thousand men. And Moses said, Consecrate yourselves to-day to Jehovah, yea, every man against his son, and against his brother; that he may bestow upon you a blessing this day. And it came to pass on the morrow, that Moses said unto the people, Ye have sinned a great sin: and now I will go up unto Jehovah; peradventure I shall make atonement for your sin." — Exodus 32:28-30 (ASV)

And the children of Levi did according to the word of Moses: and there fell of the people that day about three thousand men. For Moses had said, Consecrate yourselves today to the LORD, even every man upon his son, and upon his brother; that he may bestow upon you a blessing this day. And it came to pass on the morrow, that Moses said unto the people, You have sinned a great sin; and now I will go up unto the LORD; peradventure I shall make an atonement for your sin.

I will be bound to say that this was said after a sleepless night.

The people's sin is now so vividly before him that he begins to feel that God will be just if he punishes them and does not grant them any forgiveness. So, he goes once more up that steep climb to the top of Sinai with a trembling heart, and with only a "peradventure" on his lip.