Behold, what manner of love the Father hath bestowed upon us, that we should be called the sons of God: therefore the world knoweth us not, because it knew him not.
That is a meaty passage that reads better to me in King James, for it gets the grandeur of God's love better. We're adopted into God's family, not just forgiven.
Also, the last half of the passage is interesting. I'd be interested to dig into the Greek for know here. Spanish has two verbs for to know, one implying a loose familiarity and another for a deeper, in depth knowledge. Strong's has it down as "a knowledge grounded on personal experience."
Thus, if someone hasn't hung out with God, they aren't going to get Christians. However, if they hang out with Christians, they will start to get the hang of God if we're doing our job.