Brethren

Dictionary of Biblical Words:

Used over 200 times as a common title amongst the children of God, and given by Christ in Matt. 23:88But be not ye called Rabbi: for one is your Master, even Christ; and all ye are brethren. (Matthew 23:8). “One is your master, even Christ, and all ye are brethren.” It is a title that is the birthright of every member of God’s family. The “many sons” whom He brings to glory, and whom the Lord is not ashamed to call His “brethren.” To apply the name in any narrower sense is contrary to the teaching of Scripture.

Concise Bible Dictionary:

Besides the literal meaning of the term, it was used for persons morally or nationally associated together; also for those who formed the Jewish nation (Acts 2:29,3729Men and brethren, let me freely speak unto you of the patriarch David, that he is both dead and buried, and his sepulchre is with us unto this day. (Acts 2:29)
37Now when they heard this, they were pricked in their heart, and said unto Peter and to the rest of the apostles, Men and brethren, what shall we do? (Acts 2:37) where the expression “Men and brethren” should be translated simply “Brethren”; Rom. 9:33For I could wish that myself were accursed from Christ for my brethren, my kinsmen according to the flesh: (Romans 9:3)). It was applied by the Lord to His disciples: “Go to my brethren, and say unto them, I ascend to my Father, and your Father; and to my God, and your God” (John 20:1717Jesus saith unto her, Touch me not; for I am not yet ascended to my Father: but go to my brethren, and say unto them, I ascend unto my Father, and your Father; and to my God, and your God. (John 20:17)). “He is not ashamed to call them brethren” (Heb. 2:1111For both he that sanctifieth and they who are sanctified are all of one: for which cause he is not ashamed to call them brethren, (Hebrews 2:11); Psa. 22:2222I will declare thy name unto my brethren: in the midst of the congregation will I praise thee. (Psalm 22:22)). The Lord has placed the Christian in His own relationship as man with His Father and God, and “He that sanctifieth and they who are sanctified are all of one.” In accordance with this the saints are constantly addressed in the Epistles as “brethren,” and referred to in the Acts as “the brethren.”