Romans 16:17

Now I beseech you, brethren, mark them which cause divisions and offences contrary to the doctrine which ye have learned; and avoid them.

The brethren are commanded to mark or recognize those who cause divisions and offenses by teaching or leading into conduct contrary to the doctrine they have learned, and to avoid them or turn away from them.
Such dividers do not serve Jesus Christ, the Lord Jesus Christ.
They serve their own belly.
By good words and fair speeches they deceive the hearts of the simple and unsuspecting.
Behind them Satan works with all deceivableness of unrighteousness, striving to lead men and women to deny the faith.
Those whose obedience is known abroad, whose obedience has come abroad, are to be wise unto that which is good and innocent or simple concerning evil.

Watchmen in the Lord's cause must earnestly contend for the faith once delivered to the saints and hold fast to the One who gives power to become the children of God, without weakening their presentation of evidence in regard to the dangers of the present time.
Those who suppose themselves fitted to counsel and teach others while still needing to learn truth from the great Teacher are building on a sandy foundation.
Believers are to have life hid with Christ in God and learn truth from the great Teacher, and obedience to the truth sanctifies the soul, making men and women Christlike in thought, word, and deed and producing earnest, wholehearted, sensible people whose habits, practices, and ideas are brought into conformity to the Word and who stand in defense of the truth.
God is of power to establish believers according to the gospel and the preaching of Jesus Christ, according to the revelation of the mystery kept secret since the world began but now made manifest by the Scriptures of the prophets according to the commandment of the everlasting God and made known to all nations for the obedience of faith, to God only wise be glory through Jesus Christ forever.

The command requires all in responsible positions to realize their accountability under the eye of an all-seeing God, to be swift to hear and slow to speak and slow to wrath, to be guarded in taking responsibilities and uttering sentiments, and to keep silence when intellect is not sanctified to discern spiritual things, so that unity and perfect oneness are preserved in God's work including the ministry of the Word and medical missionary work.
The warning applied to Stephen Haskell and his wife as not sound in the faith because they caused division, working as a sly undercurrent as unconscious co-workers with evil angels, with confusion and death marking their track and scattering evil, error, and division in every place entered, and God reads the heart and marks all these divisive doings.
Their erroneous views about mortifying the flesh lead to deadly evils and destruction of souls and hasten and strengthen moral pollution instead of increasing moral purity, destroy confidence in the visions and in those in charge of the work at Battle Creek, and strengthen the hands of Stephen Smith in rebellion and of other disaffected rebels while filling conscientious, self-denying, fearful souls with error.
In contrast, those baptized with the third angel's message dwell on precious saving truth, are led out and purified through the truth and fitted for translation, and receive sleep and nourishing, strengthening food from God.
The warning applies to self-appointed messengers who claim divine guidance while working to tear down what God has established; believers are not to trust them, fellowship with them, or accept their message.