Question: How could Christ, who was crucified on Friday and rose on Sunday, have been in the grave for "three days and three nights"?
Response: This is a cultural thing (actually two cultural things). In the ancient world (Hebrew, Greek, Roman, anyway) they had a tendency to count "inclusively" - which makes a certain amount of sense. After all, if I send my son to the hardware store, telling him to get enough fence posts to put one every five feet in our hundred foot fence, I would hope he would NOT do division, but would rather count inclusively and bring back 21 posts, not 20 - the end is just as important as the beginning. Assuming Christ was crucified on Friday, Friday, Saturday and Sunday are in fact three days. One can quibble and say that unless we measure from, say exactly 3:11 PM on Friday (the ninth hour) until 3:11 PM three days later (Monday afternoon), then there was no literal fulfillment. But it is best to put ourselves in the shoes (or sandals) of the people of that time. In one sense, our tendency toward hyper-literal quantification is really no more accurate than their more general approximation of quantities (of which this "three days and three nights" is an example). Technically, unless Christ was "in the grave" for exactly three days to the nanosecond, then the prophecy is also "literally" wrong (because it would be MORE than 3/3). Also, we know that Christ gave up His spirit before sundown on Friday (the ninth hour) so the smooth 3/3 expression of the prophecy breaks down here too (i.e., you don't start and stop with a day or night beginning). Very often in the Old and New Testaments we find places where the word "all" is used in ways that trouble us, because our "all" is more stringent than their "all". It's like this: if a Hebrew boy drank a glass of milk but left a swallow in the bottom, he might well say "I drank it all"; we would object "there's still a swallow-full in the bottom of the cup!" But if our kid drinks the glass and leaves no swallow-full - yet there is still a coating of milk on the sides and drops on the bottom which are rolling around in the bottom - well, for us, that IS "all"; in reality BOTH are all (from the cultural perspective of either side), and yet NEITHER is all (if you want to get hyper-technical about it). A day in the ancient world consisted of a-day-and-a-night (or the reverse in Hebrew). If you have a significant foot in all three, then you have "three-days-and-three-nights". It may not satisfy our cultural definitions, but it does fulfill the prophecy in Hebrew terms perfectly.
Please also see the following links:
The Three Days in the Grave (in Bible Basics 4A: Christology)
Wednesday, Thursday or Friday?
Friday versus Thursday Crucifixion.
Yours in Jesus Christ,