Along with the one-thousand soldiers from each of the tribes that Moses sent to fight the war with Midyan, he also sent Pinchas who had succeeded in stopping the plague that broke out as a result of Israel falling prey to the enticement of the women of Midian and Moav, as described the end of the Torah portion of Balak. Pinchas being sent to war confirms a statement by the Sages that the merit of a mitzvah goes primarily to the one who finishes it.