Luther: "We have the promise and hope of heaven, and the recompense and reward of our present misery will be so great that we shall rebuke ourselves severely for ever having dropped one tear or sigh on account of this contempt and ingratitude of the world. Why, we shall say, did we not suffer even worse things? I never would have believed that there could be such surpassing glory in eternal life; else I should not have so dreaded to suffer even much worse things." (St. L. II: 1237; Erl., Exeg. Opp. Lat. 9, 235.)
-- Pieper, Francis. Christian Dogmatics, Vol. III. Saint Louis (Concordia Publishing House): 1953.

Many are led either by pride, dislike, or rivalry to the conviction that they can profit enough from private reading and meditation; hence they despise public assemblies and deem preaching superfluous. But, since they do their utmost to sever or break the sacred bond of unity, no one escapes the just penalty of this unholy separation without bewitching himself with pestilent errors and foulest delusions.
-- John Calvin, Institutes of the Christian Religion, IV.i.5 quotes in Hugh T. Kerr, ed., Calvin's Institutes: A New Compend, 132.

Discussing the mystery of the Incarnation, Luthardt voices the correct principle (which, however, he does not consistently follow): “The reality is not based on our thinking and our ability to comprehend it, but we must adjust our thinking to the facts. Our conceptions do not determine the facts, as the old sophists taught, but the facts determine our conceptions,” (Christl. Glaubenslehre, 1898, p. 350 f.) The “old sophists” have, sad to say, many followers. All deviations from the Christian doctrine spring from the propensity of men to make their own thoughts the measure of things and accordingly “correct” the facts of God’s Word. [...] Since man after the Fall no longer accepts God as the Center of his life and thinking, he has in foolish self-conceit made himself the center and measure of things. That is the bane of our day, particularly of our “scientific theology.”
-- Pieper, F. (1999, c1950, c1951, c1953). Christian Dogmatics (electronic ed.). St. Louis: Concordia Publishing House.

We are not to conceive the Christian faith as a bare knowledge of God which rattles around the brain and affects the heart not at all... But it is a form and solid confidence of the heart by which we securely repose in God's mercy promised us through the Gospel.
-- John Calvin, 1538 Catechism, Art. 14 quoted by I. John Hesselink's "Calvin's Theology" in McKim, Donald K., Ed., The Cambridge Companion to John Calvin, Cambridge (Cambridge Univ. Press): 2004, 86.