I do not write to you because you do not know the truth, but because you do know it and because no lie comes from the truth.
NIV
I write to you not because you are ignorant and do not perceive and know the Truth, but because you do perceive and know it, and [know positively] that nothing false (no deception, no lie) is of the Truth.
AMP
I have not written unto you because ye know not the truth, but because ye know it, and that no lie is of the truth.
KJV
But if anyone obeys his word, love for God is truly made complete in them. This is how we know we are in him:
NIV
But he who keeps (treasures) His Word [who bears in mind His precepts, who observes His message in its entirety], truly in him has the love of and for God been perfected (completed, reached maturity). By this we may perceive (know, recognize, and be sure) that we are in Him:
AMP
But whoso keepeth his word, in him verily is the love of God perfected: hereby know we that we are in him.
KJV
If you know that he is righteous, you know that everyone who does what is right has been born of him.
NIV
If you know (perceive and are sure) that He [Christ] is [absolutely] righteous [conforming to the Father's will in purpose, thought, and action], you may also know (be sure) that everyone who does righteously [and is therefore in like manner conformed to the divine will] is born (begotten) of Him [God].
AMP
If ye know that he is righteous, ye know that every one that doeth righteousness is born of him.
KJV
Dear friends, I am not writing you a new command but an old one, which you have had since the beginning. This old command is the message you have heard.
NIV
Beloved, I am writing you no new commandment, but an old commandment which you have had from the beginning; the old commandment is the message which you have heard [the doctrine of salvation through Christ].
AMP
Brethren, I write no new commandment unto you, but an old commandment which ye had from the beginning. The old commandment is the word which ye have heard from the beginning.
KJV
I am writing to you, fathers, because you know him who is from the beginning. I am writing to you, young people, because you have overcome the evil one.
NIV
I am writing to you, fathers, because you have come to know (recognize, be aware of, and understand) Him Who [has existed] from the beginning. I am writing to you, young men, because you have been victorious over the wicked [one]. I write to you, boys (lads), because you have come to know (recognize and be aware) of the Father.
AMP
I write unto you, fathers, because ye have known him that is from the beginning. I write unto you, young men, because ye have overcome the wicked one. I write unto you, little children, because ye have known the Father.
KJV