John Owen, the eminent Puritan pastor and theologian who served as a chaplain to Oliver Cromwell, once said, “If we would defend ourselves against apostasy, we must first of all be concerned for the glory of God…pray continually…contend for the faith (Jude 3)…keep careful watch over our hearts (Prov.4:23)…beware of trusting in the outward privileges of the church…and test to see if we are benefiting from the ordinances of the gospel.” 
Seven characters of false teachers:
- False teachers are men-pleasers. (Jer.5:30-31)
- False teachers are notable in casting dirt, scorn, and reproach upon the persons, name, and credits of Christ’s most faithful ambassadors. (Num.16:3; 1 Kin.22:10-26; Matt.27:62-63)
- False teachers are inventors of the devices and visions of their own heads and hearts. (Jer.14:14)
- False teachers easily pass over the great and weighty things both of Law and Gospel and stand most upon those things that are of the least concern to the souls of men. (Matt.23:2-3; 1 Tim.6:3-5)
- False teachers cover and color their dangerous principles and soul impostures with fair speeches and plausible pretenses. (Num.24:17)
- False teachers strive more to win over men to their opinion than to better them in their conversations. (Matt.23:15)
- False teachers make merchandise of their followers. (2 Pet.2:1-3)
What are the dangers of false teaching?
False teaching is dangerous for many reasons. Paul identifies several serious dangers.
- It promotes and provokes controversy rather than faith in Christ. (1 Tim.1:3-4)
- It leads to spiritual shipwreck and moral catastrophe like that of King Saul, Judas, and Demas. (1 Tim.1:19ff)
- It leads to apostasy and falling victim to demonic activity. (1 Tim.4:1-4)
- It engenders greed and discontentment, and ultimately results in ruin and destruction. (1 Tim.6:6-10)
- It results in shallowness of character, emptiness, and false knowledge. (1 Tim.6:20-21)
- It possesses a gangrene-like effect that multiplies and spreads throughout the whole body, destroying vital tissue, leading to division, decline, and, finally, death in a church. (2 Tim.2:17ff)
- It corrupts the mind and defiles the conscience, so that one’s decisions and attitudes are no longer a reliable guide to faith and purity. (Titus 1:13-16)
How do you guard yourself from false teaching?
- Be sure that you possess true, genuine, saving faith. In other words, make sure that you have been truly converted. The unconverted mind is unwilling to submit to sound doctrine (Phil.3:18; Titus 1:16; 1 Cor.2:6-7, 14; 2 Cor.4:4-6; Rom.6:17; 2 Tim.4:3-5).
- Be intent on doing God’s will as it is revealed to you in Scripture (John 7:17). A true understanding of doctrine will not come unless one is inwardly yielded to the truth he hears.
- Be mindful and diligent in giving God your best, so that when you meet God’s inspection, you will stand the test and be approved, having no need for shame because of faulty workmanship (2 Tim.2:15).
 Apostasy from the Gospel, John Owen, Puritan Paperbacks, Banner of Truth Trust
 Thomas Brooks, Precious Remedies Against Satan’s Devices, pp.230-234