John Gill Commentary Joshua 23:12

"Else if ye do at all go back, and cleave unto the remnant of these nations, even these that remain among you, and make marriages with them, and go in unto them, and they to you;" — Joshua 23:12 (ASV)

Else if you do in any wise go back
From the Lord and his worship, from his word and ordinances:

and cleave unto the remnant of these nations, [even] those that remain
among you ;
in cities not taken, or in several which the Philistines were in possession of, or lived among them as tributaries to them, if they should take to them, and be free and familiar with them, which may lead on to nearer connections in civil and religious matters:

and shall make marriages with them ;
marry their daughters to the sons of Canaanites, or admit the daughters of Canaanites to be married to their sons:

and go in unto them, and they to you ;
which is expressive of the consummation of marriage, and of the performance of the conjugal duty,