From Gills exposition of the entire bible.
So shall the Son of man be three days and three nights in the heart of the earth. That Christ means himself by the "son of man", there is no reason to doubt; and his being laid in a tomb, dug out of a rock, is sufficient to answer this phrase, "the heart of the earth", in distinction from the surface of it; but some difficulty arises about the time of his continuing there, and the prediction here made agreeable to the type: for it was on the sixth day of the week, we commonly call "Friday", towards the close, on the day of the preparation for the sabbath, and when the sabbath drew on, that the body of Christ was laid in the sepulchre; where it lay all the next day, which was the sabbath of the Jews, and what we commonly call "Saturday"; and early on the first of the week, usually called "Sunday", or the Lord's day, he rose from the dead; so that he was but one whole day, and part of two, in the grave. To solve this difficulty, and set the matter in a clear light, let it be observed, that the three days and three nights, mean three natural days, consisting of day and night, or twenty four hours, and are what the Greeks call "night days"; but the Jews have no other way of expressing them, but as here; and with them it is a well known rule, and used on all occasions, as in the computation of their feasts and times of mourning, in the observance of the passover, circumcision, and divers purifications, that , "a part of a day is as the whole" (n): and so, whatever was done before sun setting, or after, if but an hour, or ever so small a time, before or after it, it was reckoned as the whole preceding, or following day; and whether this was in the night part, or day part of the night day, or natural day, it mattered not, it was accounted as the whole night day: by this rule, the case here is easily adjusted; Christ was laid in the grave towards the close of the sixth day, a little before sun setting, and this being a part of the night day preceding, is reckoned as the whole; he continued there the whole night day following, being the seventh day; and rose again early on the first day, which being after sun setting, though it might be even before sun rising, yet being a part of the night day following, is to be esteemed as the whole; and thus the son of man was to be, and was three days and three nights in the grave; and which was very easy to be understood by the Jews; and it is a question whether Jonas was longer in the belly of the fish.
