Of faith's subjective nature we have what is almost a formal definition in the description of it as an ‘assurance of things hoped for, a conviction of things not seen’ (Heb. 11:1). It obviously contains in it, therefore, an element of knowledge (Heb. 11:6), and it as obviously issues in conduct (Heb. 11:8, cf. 5:9, 1 Pet. 1:22). But it consists neither in assent nor in obedience, but in a reliant trust in the invisible Author of all good (Heb. 11:27), in which the mind is set upon the things that are above and not on the things that are upon the earth (Col. 3:2, cf. 2 Cor. 4:16–18, Mt. 6:25.
The examples cited in Heb. 11 are themselves enough to show that the faith there commended is not a mere belief in God’s existence and justice and goodness, or crediting of His word and promises, but a practical counting of Him faithful (11:11), with a trust so profound that no trial can shake it (11:35), and so absolute that it survives the loss of even its own pledge (11:17).
So little is faith in its biblical conception merely a conviction of the understanding, that, when that is called faith, the true idea of faith needs to be built up above this word (Jas. 2:14 ff.). It is a movement of the whole inner man (Rom. 10:9, 10), and is set in contrast with an unbelief that is akin, not to ignorance but to disobedience (Heb. 3:18, 19, Jn. 3:36, Rom. 11:20, 30, 15:31, 1 Thess. 1:8, Heb. 4:2, 6, 1 Pet. 1:7, 8, 3:1, 20, 4:18, Acts 14:2, 19:9), and that grows out of, not lack of information, but that aversion of the heart from God (Heb. 3:12) which takes pleasure in unrighteousness (2 Thess. 2:12), and is so unsparingly exposed by our Lord (Jn. 3:19, 5:44, 8:47, 10:26).
In the breadth of its idea, it is thus the going out of the heart from itself and its resting on God in confident trust for all good. But the scriptural revelation has to do with, and is directed to the needs of, not man in the abstract, but sinful man; and for sinful man this hearty reliance on God necessarily becomes humble trust in Him for the fundamental need of the sinner—forgiveness of sins and reception into favor.
In response to the revelations of His grace and the provisions of His mercy, it commits itself without reserve and with abnegation (renouncing) of all self-dependence, to Him as its sole and sufficient Savior, and thus, in one act, empties itself of all claim on God and casts itself upon His grace alone for salvation.
Benjamin B. Warfield, The Works of Benjamin B. Warfield: Biblical Doctrines, vol. 2 (Bellingham, WA: Logos Bible Software, 2008), 501–502.