Adam Clarke's Commentary on the Bible - Genesis 15:16
In the fourth generation - In former times most people counted by generations, to each of which was assigned a term of years amounting to 20, 25, 30, 33, 100, 108, or 110; for the generation was of various lengths among various people, at different times. It is probable that the fourth generation here means the same as the four hundred years in the preceding verse. Some think it refers to the time when Eleazar, the son of Aaron, the son of Amram, the son of Kohath, came out of Egypt, and... read more
Adam Clarke's Commentary on the Bible - Genesis 15:15
Thou shalt go to thy fathers in peace - This verse strongly implies the immortality of the soul, and a state of separate existence. He was gathered to his fathers - introduced into the place where separate spirits are kept, waiting for the general resurrection. Two things seem to be distinctly marked here: The soul of Abram should be introduced among the assembly of the first-born; Thou shalt go to thy fathers in peace. 2. His body should be buried after a long life, one hundred and... read more