This should be joined with the preceding words, indicating the duration of his stay in the wilderness, not of his temptation, as A. V., being forty days tempted. Read as Rev., in the wilderness during forty days.
The devil
See on Mat 4:1.
He did eat nothing
Mark does not mention the fast. Matthew uses the word νηστεύσας, having fasted, which, throughout the New Testament, is used of abstinence for religious purposes; a ritual act accompanying seasons of prayer.