Go back. Literally, return. Cleave. A word (see Joshua 23:8) signifying close and intimate relationship. And the intimacy of the relationship is indicated, as in Joshua 23:8, by the use of the preposition בְּ.
Make marriages with them. No closer or more intimate relationship is possible than this. Nothing, therefore, would be more certain to draw the Israelites away from their allegiance to God, and to seduce them and their children into the false and corrupt worship of the nations around them.
"Unde deprecor vos qui fidelis estis, ut ita vitam vestram et conversationem servetis, ne in aliquo vel ipsi scandalum patiamini vel aliis scandalum faciatis; sit in vobis summi studii, summaeque cautelae, ne quis in hanc sanctam congregationem vestram pollutus introeat".
Go in unto them. Rather, go among them. Spoken of the familiar intercourse of friendship. It is equivalent to our words "associate with them."