In a previous post on the nature of saving faith, I have expounded a bit on the element of cognitio which is basic to the concept of saving faith. In this post, I would continue with Witsius' second element of saving faith: Assentia, which has been alluded to already in the previous post.
XI. To this knowledge must be joined assent, which is the second act of faith, whereby a person receives and acknowledges as truths those things which he knows, receiving the testimony of God, and thus setting to his seal, that God is true, John iii. 33. This assent is principally founded on the infallible veracity of God, who testifies of himself and of his Son, 1 John v. 9, 10. On which testimony revealed in scripture, and shedding forth all around the rays of its divinity, the believers relies with no less safety than if he had been actually present at the revelation of these things. For when the soul, enlightened by the Spirit, discerns those divine truths, and in them a certain excellent theoprepy, or beauty worthy of God, and a most wise and inseparable connection of the whole, it cannot but assent to a truth that forces itself upon him with so many arguments, and as securely admit what it thus knows, for certain, as if it had seen it with its own eyes, or handled it with its own hands, or had been taken up into the third heavens, and heard it immediately from God's own mouth. Whatever the lust of the flesh may murmur, whatever vain sophists may quibble and object, though perhaps the soul may not be able to answer or solve all objections, yet it persists in the acknowledgment of this truth, which it saw too clearly, and heard too certainly, as it were from the mouth of God, ... . And this faith is accompanied with ύποστασις, substance, and βεγχος [sic] evidence, Heb. xi. 1. and πληροφορια, full persuasion or assurance, Rom. iv. 21. (III.7.11. Vol. 1, pp. 377-378. Emphases original)
Assent according to Witsius consists in "receiving the testimony of God, and thus setting to his seal, that God is true". Not only is there knowledge of what is true (cognitio), but such knowledge must be taken to be sealed in the person who knows that truth based upon the "infallible veracity of God", not mere human reasoning. In other words, saving "assent" does not function in the same manner as the "assent" which functions according to the framework of humanistic rationalism — that "assent" which only accepts whatever is true based upon what seems "rational" to fallible human presuppositions. Rather, saving "assent" functions out of the axiom of God and of His Word, and receives Christianity as true because that is its epistemic foundation. (ie. Christianity is not be argued for, but argued from).
This assentia manifests in new believers in an interesting way, which Witsius utilizing 2 Peter 1: 16, 18 speaks of: that believers "perhaps ... may not be able to answer or solve all objections, yet it persists in the acknowledgment of this truth, which it saw too clearly, and heard too certainly, as it were from the mouth of God". Just as cognitio does not require complete knowledge of God and the Faith, neither are they required for the aspect of assentia. Ironically therefore, assentia has the dubious honor of making new believers (and believers also) seemingly stupid and foolish in the eyes of the world. Barring the few Christians scholars and theologians and philosophers, who through Spirit-given wisdom silence the unregenerate and earn their hatred, most Christians will look like anti-intellectual fools in the eyes of the world. Nevertheless, as Scripture says, "For the foolishness of God is wiser than men", it is better to be foolish on God's side, than wise on Man's side.