John Gill Commentary Deuteronomy 11:27

"the blessing, if ye shall hearken unto the commandments of Jehovah your God, which I command you this day;" — Deuteronomy 11:27 (ASV)

A blessing, if you obey the commandments of the Lord your God ,
&c.] That is, a blessing should come upon them, even all temporal blessings they stood in need of; they should be blessed in body and estate, in their families, and in their flocks, in town and country; see (Deuteronomy 28:1–6) ,

which I command you this day ;
afresh repeated to them, and enjoined them the observation of it in the name of the Lord.