For both he that sanctifieth and they who are sanctified are all of one: for which cause he is not ashamed to call them brethren,
He that sanctifieth - Christ, who once for all consecrates His people to God (Jude, bringing them nigh as the consequence) and everlasting glory, by having consecrated Himself for them in being made "perfect (as their expiatory sacrifice) through sufferings" (Hebrews 2:10). God, in electing love, through Christ's finished work, perfectly sanctifies them to God's service and to heaven once for all: then they are progressively sanctified by the transforming Spirit. 'Sanctification is glory in embryo: glory is sanctification come to the birth' (Alford).
They who are sanctified, х hoi (G3588) hagiazomenoi (G37)] - 'they that are being sanctified' (cf. "sanctified," 1 Corinthians 7:14).
Of one - Father, God: not in the sense wherein He is Father of all beings, as angels; for these are excluded by the argument, Hebrews 2:16; but as He is Father of His spiritual human sons, Christ the older Brother, and His believing people, the members of the family. This and the following verses justify His having said, " many sons" (Hebrews 2:10). "Of one" is not 'of one father, Adam,' or 'Abraham,' as Bengel, etc.; for the Saviour's participation in the lowness of our humanity is not mentioned until Hebrews 2:14, and then as a consequence of what precedes.
Moreover, 'sons of God' is the dignity obtained by our union with Christ: our brotherhood with Him flows from God being His and our Father. Christ's Sonship (by generation) in relation to God is reflected in the sonship (by adoption) of His brethren.
He is not ashamed - though being the Son of God, since they now by adoption have a like dignity, so that His majesty is not compromised by brotherhood with them (cf. Hebrews 11:16). Christianity unites such amazing contrasts as 'our brother and our God.' 'God makes of sons of men sons of God, because God hath made of the Son of God the Son of man,' (Augustine on Psalms 2:1-12.)