'Brethren' in the Bible

If you warn the brethren of these dangers you will be a good and faithful servant of Christ Jesus, inwardly feeding on the lessons of the faith and of the sound teaching of which you have been, and are, so close a follower.

And those who have believing masters should not be wanting in respect towards them because they are their brethren, but should serve them all the more willingly because those who profit by the faithful service rendered are believers and are friends.