3 It is written in the Gospel, of the mother and brethren of Christ, that is, His kindred after the flesh, that, when word had been brought to Him, and they were standing without, because they could not come to Him by reason of the crowd, He made answer, “Who is My mother? Or who are My brethren? And stretching forth His Hand over His disciples, He says, These are My brethren: and whosoever shall have done the will of My Father, that man is to Me brother, and mother, and sister.” What else teaching us, than to prefer to kindred after the flesh, our descent after the Spirit: and that men are not blessed for this reason, that they are united by nearness of flesh unto just and holy men, but that, by obeying and following, they cleave unto their doctrine and conduct.
Therefore Mary is more blessed in receiving the faith of Christ, than in conceiving the flesh of Christ. For to a certain one who said, “Blessed is the womb, which bare You,” He Himself made answer, “Yea, rather, blessed are they who hear the Word of God, and keep it.” Lastly, to His brethren, that is, His kindred after the flesh, who believed not in Him, what profit was there in that being of kin? Thus also her nearness as a Mother would have been of no profit to Mary, had she not borne Christ in her heart after a more blessed manner than in her flesh.
Source: On Holy Virginity (New Advent)