Albert Barnes Commentary 1 John 3:11

"For this is the message which ye heard from the beginning, that we should love one another:" — 1 John 3:11 (ASV)

For this is the message. The marginal reading is commandment. In the received text, this is aggelia—a message brought; in several manuscripts, and in later editions, it is epaggelia—annunciation, announcement; an order given, or a commandment (Acts 23:21). It is not very significant which reading is followed. The word command or rule would express the meaning with sufficient clarity. The reference is to the law given by the Savior as a permanent direction to His disciples.

That you heard from the beginning, that we should love one another. See Barnes on John 13:34, John 13:35; and 1 John 2:7.