The sea saw it - The word it is supplied, not very properly, by our translators. It would be more expressive to say, “The sea saw:” that is, The sea - (the Red Sea) - saw the mighty movement - the marshalled hosts - the moving masses - the cattle - the pursuing enemies - the commotion - the agitation - on its usually quiet shores. We are to conceive of the usual calmness of the desert - the waste and lonely solitudes on the banks of the Red Sea - and then all this suddenly broken in upon by vast hosts of men, women, children, and cattle, fleeing in consternation, followed by the embattled strength of Egypt - all rolling on tumultuously to the shore. No wonder that the sea is represented as astonished at this unusual spectacle, and as fleeing in dismay.
And fled - As if affrighted at the approach of such an host, coming so suddenly upon its shores.
Jordan was driven back - Referring to the dividing of the waters of the Jordan when the children of Israel passed over to the promised land. Joshua 3:13-17. They also seemed astonished at the approach of the Hebrews, and retired to make a way for them to pass over.