John the Apostle
1 John 3:23BSB·traditional attribution

And this is His commandment: that we should believe in the name of His Son, Jesus Christ, and we should love one another just as He commanded us.

John Calvin Reformed @genevareformer

23 And this is his commandment He again accommodates a general truth to his own purpose. The meaning is, that such is the discord between us and God, that we are kept off from an access to him, except we are united by love to one another. At the same time he does not here commend love alone, as before, but joins it as the companion and attendant of faith.

Matthew Henry Presbyterian @wholebiblehenry

The apostle, having mentioned keeping the commandments, and pleasing God, as the qualification of effectual petitioners in and with Heaven, here suitably proceeds, I. To represent to us what those commandments primarily and summarily are; they are comprehended in this double one: And this is his commandment, That we should believe on the name of his Son Jesus Christ, and love one another, as he gave us commandment, Jo1 3:23.

Commenting on 1 John 3:23-24

John Gill Reformed Baptist @doctorgill

And he that keepeth his commandments,.... Attends to those instructions and declarations concerning faith in Christ, and love to the brethren, and acts according to them: dwelleth in him, and he in them; that is, he dwells in Christ, and Christ dwells in him; the same is said of believing in Christ under the figurative expressions of eating his flesh, and drinking his blood; see...