Deuteronomy 22:10 - Clarke's commentary and critical notes on the Bible

Thou shalt not plow with an ox and an ass together. Thou shalt not plough with an ox and an ass - It is generally supposed that mixtures of different sorts in seed, breed, etc., were employed for superstitious purposes, and therefore prohibited in this law. It is more likely, however, that there was a physical reason for this; two beasts of a different species cannot associate comfortably together, and on this ground never pull pleasantly either in cart or plough; and every farmer knows that it is of considerable consequence to the comfort of the cattle to put those together that have an affection for each other. This may be very frequently remarked in certain cattle, which, on this account, are termed true yoke-fellows. After all, it is very probable that the general design was to prevent improper alliances in civil and religious life. And to this St. Paul seems evidently to refer, 2 Corinthians 6:14 : Be ye not unequally yoked with unbelievers; which is simply to be understood as prohibiting all intercourse between Christians and idolaters in social, matrimonial, and religious life. And to teach the Jews the propriety of this, a variety of precepts relative to improper and heterogeneous mixtures were interspersed through their law, so that in civil and domestic life they might have them ever before their eyes.