Sforno on Exodus 11:2/ספורנו על שמות י״א:ב׳

1דבר נא באזני העם וישאלו, they needed to be encouraged to ask for this as they might have worried about the Egyptians pursuing them in order to retrieve their riches. It worked in reverse; the very fact that the Egyptians chased after the Israelites, i.e. reneged, was the immediate reason G’d came to the Israelites’ assistance and drowned their pursuers. That is what made them absolutely free.