1-john 3:23

That we should believe on the name of his Son - We are commanded to believe on Christ, that for the sake of his passion and death we may be justified from all things from which we could not be justified by the law of Moses; and being through him redeemed from the guilt of sin, restored to the Divine favor, and made partakers of the Holy Ghost, we are enabled to love one another as he gave us commandment; for without a renewal of the heart, love to God and man is impossible, and this renewal comes by Christ Jesus.

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 the notes at Mark 16:16. Compare John 16:1; Acts 16:31.

And love one another ... - This follows from the other, and hence they are mentioned as together constituting his commandment. Notes, John 13:35.

3:23 And this is his commandment - All his commandments in one word. That we should believe and love - in the manner and degree which he hath taught. This is the greatest and most important command that ever issued from the throne of glory.If this be neglected, no other can be kept: if this be observed, all others are easy.