Behold, how great a love the Father has bestowed on us, that we should be called children of God! For this cause the world doesn't know us, because it didn't know him.
therefore the world knoweth us not, because it knew him not: "Therefore" is translated "for this cause" or "for this reason" in other translations. The cause or reason is given after the word "because." "The world" refers to the people of the evil world-system, which militates against God and godly things (1 John 2:15-17). Those who are getting after the world with all their being do not and cannot "know us" who are pursuing the course of righteousness. "Know" is ginosko and speaks of a knowledge acquired through experience. The world cannot fully understand and appreciate Christian people, "because it knew him not." The people of this evil system did not know God nor Jesus Christ, His Son; how can they know God’s children? To know a person in this sense requires an intimate fellowship with that person. The world does not have or desire that fellowship. Lenski says,