According to Scripture, this [Biblical] faith brings its own certainty with it. It is the assurance (ύποστασις) of things hoped for and the conviction (έλεγχος) of things not seen (Heb. 11:1), not because it is inherently so solid and firm but because it is grounded in God’s testimony and promise, as the sequel of Hebrews 11 clearly teaches. It makes the invisible goods of salvation utterly certain for us; indeed, even much more certain than one’s own insight or a given scientific proof could ever make it.
Reformed Dogmatics Vol. 1: Prolegomena (Grand Rapids, Michigan; Baker Academic; 2003) p. 573.