John Calvin Commentary Hebrews 11:29

"By faith they passed through the Red sea as by dry land: which the Egyptians assaying to do were swallowed up." — Hebrews 11:29 (ASV)

By faith they passed, etc. It is certain that many in that multitude were unbelieving; but the Lord, because of the faith of a few, granted that the whole multitude should pass through the Red Sea on dry ground. However, in doing the same thing, there was a great difference between the Israelites and the Egyptians: while the former passed through safely, the latter, coming after them, were drowned. What was the source of this difference, except that the Israelites had the word of God, and the Egyptians were without it?

The argument, then, derives its force from what happened to the contrary; therefore, he says that the Egyptians were drowned. That disastrous event was the punishment for their temerity, just as, on the other hand, the Israelites were kept safe because they relied on God’s word and did not refuse to march through the midst of the waters.