The words of Martin Luther:
“[N]ot to delight in assertions, is not the character of the Christian mind: nay, he must delight in assertions, or he is not a Christian. But, (that we may not be mistaken in terms) by assertion, I mean a constant adhering, affirming, confessing, defending, and invincibly persevering. Nor do I believe the term signifies any thing else, either among the Latins, or as it is used by us at this day. And moreover, I speak concerning the asserting of those things, which are delivered to us from above in the Holy Scriptures. Were it not so, we should want neither Erasmus nor any other instructor to teach us, that, in things doubtful, useless, or unnecessary; assertions, contentions, and strivings, would be not only absurd, but impious: and Paul condemns such in more places than one. Nor do you, I believe, speak of these things, unless, as a ridiculous orator, you wish to take up one subject, and go on with another, as the Roman Emperor did with his Turbot; or, with the madness of a wicked writer, you wish to contend, that the article concerning “Free-will” is doubtful, or not necessary.
“Be skeptics and academics far from us Christians; but be there with us assertors twofold more determined than the stoics themselves. How often does the apostle Paul require that assurance of faith; that is, that most certain, and most firm assertion of Conscience, calling it (Rom. x. 10), confession, “With the mouth confession is made unto salvation?” And Christ also saith, “Whosoever confesseth Me before men, him will I confess before My Father.” (Matt. x. 32.) Peter commands us to “give a reason of the hope” that is in us. (1 Pet. iii. 15.) But why should I dwell upon this; nothing is more known and more general among Christians than assertions. Take away assertions, and you take away Christianity. Nay, the Holy Spirit is given unto them from heaven, that He may glorify Christ, and confess Him even unto death; unless this be not to assert – to die for confession and assertion. In a word, the Spirit so asserts, that He comes upon the whole world and reproves them of sin (John xvi. 8) thus, as it were, provoking to battle. And Paul enjoins Timothy to reprove, and to be instant out of season. (2 Tim. iv. 2.) But how ludicrous to me would be that reprover, who should neither really believe that himself, of which he reproved, nor constantly assert it! – Why I would send him to Anticyra, to be cured…
Unless you consider all Christians to be such (as the term is generally understood) whose doctrines are useless, and for which they quarrel like fools, and contend by assertions. But if you speak of necessary things, what declaration more impious can any one make, than that he wishes for the liberty of asserting nothing in such matters? Whereas, the Christian will rather say this – I am so averse to the sentiments of the Sceptics, that wherever I am not hindered by the infirmity of the flesh, I will not only steadily adhere to the Sacred Writings every where, and in all parts of them, and assert them, but I wish also to be as certain as possible in things that are not necessary, and that lie without the Scripture; for what is more miserable than uncertainty… The Holy Spirit is not a Sceptic, nor are what he has written on our hearts doubts or opinions, but assertions more certain, and more firm, than life itself and all human experience.”