Jamieson, Fausset and Brown on 1 John 4:9

9. toward us--Greek, "in our case."

sent--Greek, "hath sent."

into the world--a proof against Socinians, that the Son existed before He was "sent into the world." Otherwise, too, He could not have been our life (1Jo 4:9), our "propitiation" (1Jo 4:10), or our "Saviour" (1Jo 4:14). It is the grand proof of God's love, His having sent "His only-begotten Son, that we might live through Him," who is the Life, and who has redeemed our forfeited life; and it is also the grand motive to our mutual love.