John Gill Commentary Judges 1:23

"And the house of Joseph sent to spy out Beth-el. (Now the name of the city beforetime was Luz.)" — Judges 1:23 (ASV)

And the house of Joseph sent to descry Bethel
To reconnoitre the place, to observe its passes and avenues, which were most accessible, and to examine the walls of it, where they were weakest and least defended:

now the name of the city before [was] Luz ;
which signifies a "nut"; perhaps it was so called from large numbers of nut trees which grew near it; the Jews suggest it was like a nut, no entrance into it but through a cave or some subterraneous passage, see (Genesis 28:19) .