And the Lord spake unto Moses. Rather, "Now the Lord had said unto Moses." The Hebrew has no form for the pluperfect tease, and is consequently obliged to make up for the grammatical deficiency by using the simple preterite in a pluperfect sense.
We cannot definitely fix the time when Moses had received this revelation; but the expression, one plague more, shows that it was after the commencement of the "plague of darkness." When he shall let you go, he shall surely thrust you out altogether.
The Hebrew win not bear this rendering. It runs distinctly thus—"When he shall let you go altogether, he will assuredly thrust you out hence." As Canon Cook notes, "the meaning is—when at last he lets you depart, with children, flocks, herds, and all your possessions, he will compel you to depart in haste".
It has been well noticed by the same writer that both this announcement, and the previous relentings of Pharaoh, would have caused Moses to have preparations made, and to hold the Israelites in readiness for a start upon their journey almost at any moment.
No doubt a most careful and elaborate organization of the people must have been necessary; but there had been abundant time for such arrangements during the twelvemonth that had elapsed since the return of Moses from Midian.