False doctrine does not necessarily make a man a heretic, but an evil heart can make any doctrine heretical.
Doctrine
Edward McKendree (E. M.) Bounds
It is the failure, in season and out of season, to proclaim these great doctrines that accounts for their fading from sight and from faith. Every doctrine of the Bible that is not continually preached dies out of the faith of the people. Our fathers had to fight for every inch of ground on which they advanced these great truths, and this age requires a loyal and militant campaign for God’s great truths. An unsheathed sword is the only preserver and defender of God’s truth. The truth of God will flourish and conquer if its preachers have faith to boldly proclaim and courage to fight for it without compromise or wavering.
Abraham Kuyper
Satan knows that he can undermine the structure of the church by slyly removing just one fundamental doctrine at a time. He frequently loosens a large foundation gradually, chiseling it away bit by bit. That is why tolerance for the sake of peace may be dangerous. One step by giving in will lead to a next step, and will not God visit us with blindness if we deliberately darken the truth He has graciously entrusted to us. How shall we justify ourselves if we permit even a little of the truth to be laid aside? Is that ours to do? When peace is injurious to the truth, peace must give way. Peace with God is of greater value than peace with men.
John Bunyan
The truths that I know best I have learned on my knees. I never know a thing well, till it is burned into my heart by prayer.
Count Von Zinzendorf
Our method of proclaiming salvation is this: to point out to every heart the loving Lamb, who died for us, and although He was the Son of God, offered Himself for our sins… by the preaching of His blood, and of His love unto death, even the death of the cross, never, either in discourse or in argument, to digress even for a quarter of an hour from the loving Lamb: to name no virtue except in Him, and from Him and on His account-to preach no commandment except faith in Him; no other justification but that He atoned for us; no other sanctification but the privilege to sin no more; no other happiness but to be near Him, to think of Him and do His pleasure; no other self denial but to be deprived of Him and His blessings; no other calamity but to displease Him; no other life but in Him. (Count Zinzendorf is considered to be the father of Modern Missions)