"Now I beseech you, brethren, mark them which cause divisions and offenses contrary to the doctrine which ye have learned; and avoid them. For they that are such serve not our Lord Jesus Christ, but their own belly; and by good words and fair speeches deceive the hearts of the simple" (Romans 16:17,18).
In order to mark and avoid those professing Christian teachers and leaders who are promoting doctrinal heresy (thus causing divisions among Christian believers), it is obvious that we must exercise sound Biblical discernment and judgment. This judgment must be based on "the doctrine which ye have learned" from God's word. "To the law and to the testimony: if they speak not according to this word, it is because there is no light in them" (Isaiah 8:20).
Such decisions are not to be based on supposed scholarship, tolerance, or eloquence, for such teachers "by good words and fair speeches deceive the hearts of the simple." Instead, we must know and apply God's word, the Holy Scriptures. We must be like the Bereans, who, when they heard new teachings, "searched the scriptures daily, whether those things were so" (Acts 17:11).
It is sadly true today that many who call themselves Christians have compromised with the pseudo-scientific worldview of evolutionary humanism that controls all secular schools and colleges, hoping thereby to avoid the "offense of the cross" (Galatians 5:11), and to remain on good terms with "the princes of this world" and "the wisdom of this world" (I Corinthians 2:6).
They do this for their own personal gain or prestige, however, not serving Christ, "but their own belly" (Romans 16:18). Those who are "simple," Bible-believing Christians are, therefore, not to be "deceived" by their "good words," but to "mark" and "avoid" them. HMM