Ibn Ezra on Deuteronomy 20:5/אבן עזרא על דברים כ׳:ה׳

1DEDICATED IT. Chanakho (dedicated it) is similar to the word chanukkat (dedication of) in the dedication offer of the altar (Num. 7:10). The word chanokh (train) in Train up a child (Prov. 22:6) is similar. Our rabbis, of blessed memory, learned from the latter that we train (mekhannechin) children. The reason that [one who has not dedicated his house is released from service] is that such a man’s heart and desire is to dedicate his house. Look, his mind will be upon his house, not on the battle. He will therefore flee and cause others to flee.