Jamieson, Fausset and Brown on Exodus 14:3

3. the wilderness hath shut them in--Pharaoh, who would eagerly watch their movements, was now satisfied that they were meditating flight, and he naturally thought from the error into which they appeared to have fallen by entering that defile, he could intercept them. He believed them now entirely in his power, the mountain chain being on one side, the sea on the other, so that, if he pursued them in the rear, escape seemed impossible.