Personally the idea that Jessica
is a form of "Iscah" has never convinced me. The reasoning for this seems to be that since in one early English translation of the Bible "Iscah" is printed as "Jesca" that Jesca must be the source of Jessica
. But no one knows how Shakespeare came up with the name and it's always seemed to me to be more logical that he was simply creating what he thought would be an "Italianate" sounding feminine form for the prominent Old Testament name Jesse
rather than scouting around for a really obscure Old Testament female name and then modifying that.
At least a derivation from Jesse
seems just as plausible to me as a derivation from Iscah.