1 Samuel 30:25

And it was so from that day forward, that he made it a statute and an ordinance for Israel unto this day.

From that day forward a lasting statute and ordinance was established for Israel that those who remained behind to guard the supplies were to share the spoils equally with those who went into the battle. The division was to be equal between the fighters and the guards, with no distinction in their portion of the recovered goods. This arrangement was just because both groups had a part in the campaign, the one by fighting and the other by protecting what was left behind. The victory itself had been given by the Lord, so none could claim the spoil as earned by his own strength alone.