“Nothing makes a man so virtuous as belief of the truth. A lying doctrine will soon beget a lying practice. A man cannot have an erroneous belief without by-and-by having an erroneous life. I believe the one thing naturally begets the other.”

—Charles Haddon Spurgeon

“All truth is given by revelation, either general or special, and it must be received by reason. Reason is the God-given means for discovering the truth that God discloses, whether in his world or his Word. While God wants to reach the heart with truth, he does not bypass the mind.” 
Jonathan Edwards

“The truth of the Gospel is the principal article of all Christian doctrine . . . Most necessary is it that we know this article well, teach it to others, and beat it into their heads continually.”

—Martin Luther

"There may have been a day when there could be propagation of Christianity without defense. But such a day at any rate is past. At the present time, when the opponents of the gospel are almost in control of our churches, the slightest avoidance of the defense of the gospel is just sheer unfaithfulness to the Lord. There have been previous great crises in the history of the Church, crises almost comparable to this. One appeared in the second century, when the very life of Christendom was threatened by the Gnostics. Another came in the Middle Ages when the gospel of God’s grace seemed forgotten. In such times of crisis, God has always saved the Church. But He has always saved it not by theological pacifists, but by sturdy contenders for the truth.”

J. Gresham Machen (1881-1937), Christianity & Liberalism, p. 146-147