Paul had warned the doctrinally strong not to look down on the weak, and the weak not to condemn the strong. In spite of his warnings this was actually occurring, continues today and is an inexcusable sin. The apostle accusingly asks why one church member is sinning against another. These critics should bear in mind that the one whom they condemn or despise is, after all, a brother. Using the term brother indicates the seriousness of the sin that was being committed. God has declared that the person who sows seeds of discord amongst the brethren is an abomination to Him.
Proverbs 6:16–19
16 These six things doth the Lord hate: Yea, seven are an abomination unto him:17 A proud look, a lying tongue, And hands that shed innocent blood,18 A heart that deviseth wicked imaginations, Feet that be swift in running to mischief, 19 A false witness that speaketh lies, And he that soweth discord among brethren (KJV).
Content retrieved from: https://www.sermonaudio.com/sermoninfo.asp?SID=6423163514874&fbclid=IwAR3DgXhTDqtWnBh68cRhnjtKgjpVKJMUi4Q1iPs11nmqL8p5tj-iYpL1Fw4.