Mt 12:50, Mk 3:35, Lk 8:21, Rom 8:29, Ps 22:22
In the Old Testament it was foretold that Christ would proclaim the gospel of salvation to His brethren. (Ps 22:22)
Ps 22:22 I will declare thy name unto my brethren: in the midst of the congregation will I praise thee.
God sanctified us by making Jesus do the work of Christ and made us brothers and sisters of the Christ Jesus. (Heb 2:11-12, Rom 8:29)
Heb 2:11 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, 12 Saying, I will declare thy name unto my brethren, in the midst of the church will I sing praise unto thee.
Rom 8:29 For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren.
Those who do God's will, that is, those who believe in Jesus as the Christ, are the brothers of Jesus. (Jn 6:29, Mt 12:50, Mk 3:35, Lk 8:21)
Jn 6:29 Jesus answered and said unto them, This is the work of God, that ye believe on him whom he hath sent.
Mt 12:50 For whosoever shall do the will of my Father which is in heaven, the same is my brother, and sister, and mother.
Mk 3:35 For whosoever shall do the will of God, the same is my brother, and my sister, and mother.
Lk 8:21 And he answered and said unto them, My mother and my brethren are these which hear the word of God, and do it.