He (his armour-bearer) fell likewise upon his sword The same sword on which Saul had fallen, which was the sword of the armour- bearer. This will appear evident to any one that reads these two verses (the 4th and 5th) in the original. Now it is the established tradition of the Jewish nation, that this armour-bearer was Doeg, which is not at all unlikely; and if so, then both Saul and his executioner fell by that very weapon with which they had before massacred the priests of God!
Related Commentaries of 1 Samuel 31:5
1 Samuel 31:5
5 And when his armourbearer saw that Saul was dead, he fell likewise upon his sword, and died with him.