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.
God's commandments summed up in the one Gospel commandment.
This is his commandment - singular: for faith and love are not separate commandments, but indissolubly one. We cannot truly love one another without faith in Christ, nor truly believe in Him without love.
Believe - once for all [aorist, pisteusoomen (G4100), B; but 'Aleph (') A C, pisteuoomen, 'continually believe].
On the name of his Son - all that is revealed in the Gospel concerning Him, and on Himself, in His person, offices, and atoning work.
As he - Jesus.