Why did the vineyard workers hired just before sunset get a whole day's pay?
They received a full day's wage because any part of a day is considered a whole. This principle governs Scripture's reckoning of time, where a portion of a day or a year counts as complete. The parable shows that God's accounting treats even a brief span as the entire unit.
Les explains that Jesus told of hiring workers for the vineyard at morning, noon, and about an hour before sunset. The ones hired last still received the whole day's wage. The reason given is that any part of a day is considered a whole. Les then applies this to time reckoning: any part of a year is also considered a whole. He notes that this caused chronologists difficulty in reconstructing Old Testament times, because a king who reigned a little over nine years might be recorded as reigning ten years. The Bible treated that little part of the tenth year as a whole year. Les also uses this to explain how Christ could be crucified on Friday and yet be said to be in the grave three days and three nights, since going into the grave before six o'clock that evening counted as a day.