THE FIRST EPISTLE GENERAL OF JOHN - Chapter 3 - Verse 23
Verse 23. And this is his commandment. His commandment, by way of eminence; the leading, principal thing which he enjoins on 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 "Mr 16:16".
And love one another, etc. This follows from the other, and hence they are mentioned as together constituting his commandment. See Barnes "John 13:36".
{e} "this is his commandment" De 18:15-19; John 14:1