John Gill Commentary Deuteronomy 17:10

"And thou shalt do according to the tenor of the sentence which they shall show thee from that place which Jehovah shall choose; and thou shalt observe to do according to all that they shall teach thee:" — Deuteronomy 17:10 (ASV)

And you shall do according to the sentence which they of that
place which the Lord shall choose shall show you
The judges of the inferior courts were to return and proceed on the difficult case according to the judgment of the great court at Jerusalem, and follow the directions and instructions they should give them:

and you shall observe to do according to all that they inform you ;
not only observe and take notice of what they say, but put it in practice, and not in some things and some circumstances only, but in all and everything they should give them information about relating to the case in question.