Sefer HaChinuch ספר החינוך

The commandment to set up a spike to dig with: That there be to each one of the soldiers a spike — or another tool with which it is fitting to dig — suspended with his war gear, in order that he dig with it a place in the ground to take care of his needs in a way that is prepared for this. (See Sefer HaMitzvot, Positive Commandments 193 and Mishneh Torah, Kings and Wars 10.) And about this is it stated (Deuteronomy 23:14), “With your aazen you shall have a spike” — the explanation of (the word,) your aazen is your weapons.

And the root of this commandment and all of its content is in the commandment that is before it. And since this verse has come to our hand, we will write the midrash about it; that they, of blessed memory, affixed to it in the Gemara, when they said (Ketuvot 5b), “Why are the fingers of a person made like spikes?” — which is to say, tapered? “So that if a person hears a thing that is not proper, he should put his finger into his ear (ozen), as it is stated, ‘With your aazen you shall have a spike’ — do not read, ‘your aazen,’ but rather ‘your ozen.’”