David said furthermore, As the LORD lives, the LORD shall strike him; or his day shall come to die; or he shall descend into battle, and perish.
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George Leo Haydock
To die a natural death. Thus those who are slain, are said to die before their day, Psalm liv. 28. Jesus was not taken, because his hour was not yet come, John ii. 4., and vii. 30. (Calmet)
David waits with patience, that God might take off his adversary by sickness, old age, or the sword. (Menochius) -- He will not ascend the throne before the time appointed, and he will not kill Saul, except it be in battle, in his own defence. (Haydock)