It is interesting to note that our Lord never called His disciples "brethren" until after His resurrection, and our text, which identifies them as such, was the first thing He uttered after rising from the dead, at least as recorded in Scripture.
Until then He had referred to them in a variety of ways, including "little children" (John 13:33), "brethren," in the sense of brothers in a family (Matthew 12:49), and even "friends."
"Henceforth I call you not servants; for the servant knoweth not what his lord doeth: but I have called you friends; for all things that I have heard of my Father I have made known unto you" (John 15:15). Certainly the disciples held a special place in Christ’s heart.
But it was not until He had risen from the dead, He who was "the firstborn from the dead" (Colossians 1:18), the "firstfruits of them that slept" (1 Corinthians 15:20), that His disciples, and indeed all who would "believe on |Him| through their word" (John 17:20), could be made "sons of God" (Romans 8:14). "And if children, then heirs; heirs of God, and jointheirs with Christ" (Romans 8:17). This high standing comes as a fulfillment of His determination to "be the firstborn among many brethren" (v. 29).
He has relabeled the "great congregation" (Psalm 22:22, 25 quoted in Hebrews 2:12) the "church," identifying the individual members as His "brethren," and is not "ashamed" to do so (Hebrews 2:11). As we see in our text, His God is our God, His Father is our Father; in all ways, we who have believed on Him are His brothers. Oh, what a standing is ours! JDM