1st Chronicles 21:17 And David said unto God, Is it not I that commanded the people to be numbered? even I it is that have sinned and done evil indeed; but as for these sheep, what have they done? let thine hand, I pray thee, O Lord my God, be on me, and on my father's house; but not on thy people, that they should be plagued.
Both David, and many thousands in Israel had been cherishing national pride, and as their craving to be like the other nations fomented, the theocracy God initiated seemed more and more antiquated and by their estimate, insufficient. To number the people would be to demonstrate the perspective that their strength was in numbers, not in God, and no sooner than that perspective is taken and cultivated, satan would tempt them to the fatal belief, that they do not need God anymore.
Therefore, even though the seventy thousand didn’t actually number the people, they too had partaken of the same spirit, as did David, and because David hastened to repent, and they didn’t, it may seem to some minds as if God made a mistake in striking the innocent, while letting the guilty off the hook…. [Patriarchs & Prophets pp 746>748] Intercourse with heathen peoples led to a desire to follow their national customs and kindled ambition for worldly greatness.
David determined to increase his army by requiring military service from all who were of proper age. The numbering of the people would show the contrast between the weakness of the kingdom when David ascended the throne and its strength and prosperity under his rule. The prosperity of Israel under David had been due to the blessing of God rather than to the ability of her king, or the strength of her armies. But the increasing of the military resources of the kingdom would give the impression to surrounding nations that Israel’s trust was in her armies, and not in the power of Jehovah.
1st Samuel 17:45 Then said David to the Philistine, Thou comest to me with a sword, and with a spear, and with a shield: but I come to thee in the name of the Lord of hosts, the God of the armies of Israel, whom thou hast defied.
May The Lord add His blessing to the study of His word. God bless!