Albert Barnes Commentary 1 John 3:23

"And this is his commandment, that we should believe in the name of his Son Jesus Christ, and love one another, even as he gave us commandment." — 1 John 3:23 (ASV)

And this is his commandment. His commandment, preeminently; the leading, principal thing which he requires of us; the commandment which lies at the foundation of all true obedience.

That we should believe on the name of his Son Jesus Christ. See Barnes on Mark 16:16.

Compare to John 16:1; Acts 16:31.

And love one another, etc. This follows from the other, and hence they are mentioned as together constituting his commandment. See Barnes on John 13:36.