What’s the deal with all that? One explanation may be that the physical wars in the OT were signs of the spiritual warfare after Christ.
Another is that God was pursuing a very important end: preparing the world for the Incarnation of the Son. Great sacrifices had to be made in order for this momentous and highly beneficial to mankind event to succeed.
From the deontological perspective, God is the Author of life and death and has a “right” both to give life and to kill at His pleasure.
But the truth is probably even simpler. John the Baptist said, “And do not presume to say to yourselves, ‘We have Abraham as our father.’ For I tell you, God can raise up children to Abraham from these stones.” (Mt 3:9) It follows that natural unregenerated humans are almost worthless. They are a dime a dozen. They are grass, and God can mow the lawn of His creation however He wills. What does it really in the final analysis matter if I die now at Moses’ sword or 20 years from now from some hideous disease? Earthly life ends, and with it, as it appears to a faithless man, all subjectivity, experience, pleasure, understanding, and memory. If it ends a little sooner rather than later, so what?
But among this grass, there are a few flowers. God cares for them. He gives them living water; He prunes them; He increases their charity. There is a price God pays for this care; not, obviously, because He gets tired from the effort of gardening, but because He cannot grace everyone, and if He chooses Smith to be the flower, He by that very fact refrains from uplifting Jones. For mysterious reasons of divine providence, grace is fairly scarce.
These flowers “are worth more than many sparrows.” (Lk 12:7)
Now if a person has been chosen thus, then rejecting the grace is a monstrous crime, because God has forsaken others for his sake. The costs have been borne, but no profit realized. Therefore the importance of cooperating with grace cannot be overemphasized.