Hereby perceive we the love of God, because he laid down his life for us: and we ought to lay down our lives for the brethren.
What true love to the brethren is, is illustrated by Christ's to us.
Hereby - `herein.'
The love of God. "Of God" is not in the original. Translate, 'We arrive at the knowledge of LOVE;' we apprehend what true love is.
He - Christ.
And we - on our part, if necessary for the glory of God, the good of the Church, or the salvation of a brother.
Lives. Christ laid down His one life for us all: we ought to lay down our lives severally for the lives of the brethren: if not actually, at least virtually, by giving our time, care, prayers, substance: 'Non nobis, sed omnibus.' Our life ought not to be dearer to us than God's own Son was to Him. The apostles and martyrs acted on this principle.