Tafsiran Ulangan 20:5: Rashi, Chizkuni, Ibn Ezra & Sforno

ולא חנכו [WHAT MAN IS THERE THAT HATH BUILT A NEW HOUSE] AND HATH NOT DEDICATED IT — i.e. has not yet dwelt in it. The term חנך denotes beginning a thing (here, it means beginning to live in it; cf. Rashi on Genesis 14:14).

אשר בנה, “who has built;” the Torah here teaches the correct order in which young men are to approach the subject of matrimony; first they have to make a commitment to the woman they have chosen; then they have to provide for their bride a place to live in; then they have to establish a sound economic base, such as planting a vineyard. Having done so, they may proceed to complete the wedding ceremonies. The reason why such people are excused from fighting in an expansionary war, is that their worries about if they will be able to complete their plans for the future will distract them from performing their military duties to the best of their abilities. They will worry that in spite of promises from G-d they may be or have been guilty of sins which will be used by G-d to withdraw His protection from them when they are facing danger.

inaugurated it as in “the dedication of the altar” [Numbers 7: 10], and also “initiate the child” [Proverbs 22: 6] (from which our Sages, of blessed memory, derived the principle that one must educate one’s children [Qiddushin 30a]). The reason for these commandments is that his attention, and all of his desires, are directed to dedicating his house. Thus, his thoughts are on his house, and not on the battle; consequently, he will flee, and he will induce others to flee.

ואיש אחר יחנכנו [LEST HE DIE IN THE WAR] AND ANOTHER MAN DEDICATE IT — which is a matter that causes grief of mind.