To whom also he showed himself alive after his passion by many infallible proofs, being seen of them forty days…
The period is a significant space of time in Scripture, and is frequently allotted as a term of probation before some great event which concerned God's kingdom. For forty days and forty nights rain was sent upon the earth as the prelude to the Deluge. Before the giving of the law Moses was in the Mount forty days and forty nights; and when after the destruction of the first tables, the law was renewed again, Moses was with the Lord forty days and nights. The same space of time was spent by the spies who were sent forth to survey Canaan the type of the spiritual inheritance of the people of God. For forty days and nights Elijah journeyed before he came by Divine direction to Horeb the Mount of God. The time of probation and repentance given to Nineveh was a like space of time. When we come to the New Testament we note the same phenomenon. Forty days after His birth our Lord was presented in the Temple. Before He entered on the work of His ministry after His baptism He was forty days tempted in the wilderness. So now He abode on earth forty days before His ascension. What significancy there may be in the number we are not informed: the recurrence, however, of this space of time, usually in connection with events of extraordinary importance, would lead us to believe that there is a mystery in the number. Nor is this diminished when in parallelism with the forty days' wandering (Numbers 14:33, 34) Jerusalem had its forty years of trial and space for repentance after the Crucifixion;and not until that period had been accomplished was it destroyed by the Romans. For forty days during which He showed Himself alive they were obdurate, and forty years afterwards each day for a year came the destruction of the nation.
(J. Lightfoot, D. D.)
Parallel VersesKJV: To whom also he shewed himself alive after his passion by many infallible proofs, being seen of them forty days, and speaking of the things pertaining to the kingdom of God: