"... as we look not to the things that are seen but to the things that are unseen. For the things that are seen are transient, but the things that are unseen are eternal" (2 Corinthians 4:18 ESV).
"Now faith is the assurance of things hoped for, the conviction of things not seen...And without faith it is impossible to please him, for whoever would draw near to God must believe that he exists and that he rewards those who seek him" (Hebrews 11:1-6 ESV).
"In this you rejoice, though now for a little while, if necessary, you have been grieved by various trials, so that the tested genuineness of your faith—more precious than gold that perishes though it is tested by fire—may be found to result in praise and glory and honor at the revelation of Jesus Christ" (1 Peter 1:6-7 ESV).
"This is a life of faith, for God will try the truth of our faith, so that the world may see that God has such servants as will depend upon His bare word." - Richard Sibbes
"Faith, without trouble or fighting, is a suspicious faith; for true faith is a fighting, wrestling faith." - Ralph Erskine
"Faith endures as seeing Him who is invisible (Heb. 11:27); endures the disappointments, the hardships, and the heart-aches of life, by recognizing that all comes from the hand of Him who is too wise to err and too loving to be unkind. But so long as we are occupied with any other object than God Himself, there will be neither rest for the heart nor peace for the mind. But when we receive all that enters our lives as from His hand, then, no matter what may be our circumstances or surroundings—whether in a hovel or prison-dungeon, or at a martyr's stake—we shall be enabled to say, " The lines are fallen unto me in pleasant places" (Ps. 16:6). But that is the language of faith, not of sight nor of sense." - Arthur W. Pink