The question “Is Scripture adequate?” is much like the question “Is Christ adequate?” The answer depends entirely upon what one expects either to do. Each one does something specific for us; neither does everything. In one sense, God wasn’t even adequate for Adam in the garden. Though Adam was walking in unfallen fellowship with the Father, God still said, “It is not good for the man to be alone; I will make him a helper suitable for him” (Genesis 2:18).
The Bible is sufficient to give the “wisdom that leads to salvation” and to enable the godly person to be “adequate, equipped for every good work” (2 Timothy 3:15,17). Such sufficiency does not preclude other sources of learning that give further instruction in mental health and skill at living.
The Scripture is the standard of truth to be studied, applied, and cherished. The Bible itself, however, doesn’t support the “Bible only’ view. It does not teach that man is so distorted by sin as to lose his ability to discover useful truth on his own. It teaches rather that man has an extensive ability to draw from general revelation making accurate and useful assessments about life and its problems.
— Greg Koukl, from Is the Bible Sufficient?—Solid Ground, May-June, 2007, p. 4