John Gills Exposition of the Bible Commentary - 2 Samuel 15:7
And it came to pass after forty years ,.... Or four years; so long it was from the reconciliation of Absalom to David, as Josephus F6 Antiqu. l. 7. c. 9. sect. 1. says; and so read Theodoret on the place, the Syriac and Arabic versions: but some say it was either forty years from the time Israel first had a king; and which might be an era of reckoning with the Jews, as the era of Seleucidae was with the Greeks, on the like account; or from the time Saul slew the priests at Nob, as... read more
Matthew Henry's Complete Commentary - 2 Samuel 15:7-12
We have here the breaking out of Absalom's rebellion, which he had long been contriving. It is said to be after forty years, 2 Sam. 15:7. But whence it is to be dated we are not told; not from David's beginning his reign, for then it would fall in the last year of his life, which is not probable; but either from his first anointing by Samuel seven years before, or rather (I think) from the people's desiring a king, and the first change of the government into a monarchy, which might be about... read more