John Gill Commentary Joshua 8:31

"as Moses the servant of Jehovah commanded the children of Israel, as it is written in the book of the law of Moses, an altar of unhewn stones, upon which no man had lifted up any iron: and they offered thereon burnt-offerings unto Jehovah, and sacrificed peace-offerings." — Joshua 8:31 (ASV)

As Moses the servant of the Lord commanded the children of
Israel, as it is written in the book of the law of Moses
(Deuteronomy 27:5) ;

an altar of whole stones, on which no man has lift up [any] iron ;
(See Gill on Exodus 20:25), (See Gill on Deuteronomy 27:5), and, (See Gill on
Deuteronomy 27:6):

and they offered thereon burnt offerings unto the Lord, and sacrificed
peace offerings ;
by way of thanksgiving for the good land they were introduced into, and this was what they were ordered to do by Moses, (Deuteronomy 27:6Deuteronomy 27:7) .