Thou didst cleave the fountain and the flood - That is, the source of the streams and the streams themselves. The main allusion is probably to the Jordan, and the idea is, that God had, as it were, divided all the waters, or prevented any obstruction to his people from the river in any respect; as if the waters in the very springs and fountains, and the waters in the channel of the river flowing from those springs and fountains, had been so restrained and divided that there was a safe passage through them. Joshua 3:14-17.
Thou driedst up mighty rivers - Margin, “rivers of strength.” The Hebrew - איתן 'êythân - (compare Deuteronomy 21:4; Amos 5:24; 1 Kings 8:2) - means rather perennial, constant, ever-flowing. The allusion is to rivers or streams that flow constantly, or that do not dry up. It was this which made the miracle so apparent. It could not be pretended that they had gone over the bed of a stream which was accustomed to be dry at certain seasons of the year. They passed over rivers that never dried up; and, therefore, it could have been only by miracle. The main allusion is undoubtedly to the passage of the Jordan.