John Gill Commentary Deuteronomy 6:18

"And thou shalt do that which is right and good in the sight of Jehovah; that it may be well with thee, and that thou mayest go in and possess the good land which Jehovah sware unto thy fathers," — Deuteronomy 6:18 (ASV)

And you shall do that which is right and good in the sight of
the Lord
And what is such appears from the declaration of his mind and will in the commandments he has given, and obeying which is therefore doing what is right and good; for his commandment is holy, just, and good, being agreeable both to his nature and will, (Romans 7:12) that it may be well with you; as it is with those that fear God, and keep his commandments:

and that you may go in and possess the good land which the Lord
sware unto your fathers ;
to give to them and to their posterity, even the land of Canaan; but if they did not what was right and good in the sight of God, they might expect to be kept out of it, as their immediate parents were, whose carcasses fell in the wilderness.