His Commandment -- Receive His Grace in Truth

"I rejoiced greatly that I found of thy children walking in truth, as we have received a commandment from the Father." (2 John 4)

We are called to walk in the truth, the truth of the Gospel:

"5To whom we gave place by subjection, no, not for an hour; that the truth of the gospel might continue with you." (Galatians 2: 5)

and then

"14But when I saw that they walked not uprightly according to the truth of the gospel, I said unto Peter before them all, If thou, being a Jew, livest after the manner of Gentiles, and not as do the Jews, why compellest thou the Gentiles to live as do the Jews?" (Galatians 2: 14)

Keep in mind also that Jesus brought with Himself grace and truth (John 1: 17), one unified reality.

Also realize that walking in the truth is a commandment from the Father, not from a boss, or a slavemaster:

"For it became him, for whom are all things, and by whom are all things, in bringing many sons unto glory, to make the captain of their salvation perfect through sufferings." (Hebrews 2: 10)

and

"And he is the head of the body, the church: who is the beginning, the firstborn from the dead; that in all things he might have the preeminence." (Colossians 1: 18)

Now, if Jesus is the first born, there must be a second-born, third-born, etc.:

"For as many as are led by the Spirit of God, they are the sons of God. 15For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father." (Romans 8: 14-15)

He is our Father because He has adopted us as His children, and as our Father, His commandment is that we walk in His grace, the truth which sets us free (John 8: 32)