to offer sacrifices to the LORD our God.'
unless a mighty hand compels him.
with all the wonders that I will perform among them.
He also knows that the king of Egypt will not agree to this request, unless he is forced into it by a higher power. So, God plans to perform wonders among the Egyptians. Unfortunately, these wonders do not sound as if they will be beneficial towards the Egyptians, for God proclaims that He will 'strike' them with these events. Calmly, God declares that after that, Pharaoh would indeed let the Hebrews go.
Not only that, but God also plans some recompense for the years of slavery which the Israelites have endured. The Israelite women are to request gold and silver articles and clothing from their Egyptian neighbors. This 'plunder' will not be taken violently, for God will make the Egyptians favorably disposed to give it to them.
[Perhaps this is why the women were directed to perform this part of the mission. Not that women can't be just as violent as men, but just that there would be less opportunity for any type of violent 'payback' or skirmishes to erupt. Also, I notice that the women were to ask their neighbors or women living in their households for the items -- another factor which might make the Egyptians more willing to give, and the freed slaves less inclined to exact revenge.]