This is a longish quote, but there is so much wisdom here:
In forming the religious character…it is of the utmost importance that the foundation be laid in clear views of divine truth. Doctrinal knowledge is apt to be undervalued by private Christians, and especially the young. They imagine, according to the popular prejudice, that if the heart be right, and the conduct correct, the doctrines embraced are of small moment. This suppose that the heart of any one may be right, while his principles are essentially wrong; or that his practice may be pure, while his religious opinions are radically erroneous. But nothing can be more contrary both to Scripture and experience. The great Founder of our holy Religion declares that men are “sanctified by the truth.” In fact, it is only so far as the truth is received, loved and obeyed that real religion has any place either in the heart or life…. It is not intended here either to assign the reasons, or to show the sin and folly of this deplorable fact; but to remark that the foundation of this fact is commonly laid in youth. If the young, and even the thinking and serious portion of the young, were as careful to store their minds with elementary principles, and with clear, discriminating views of revealed truth, as they are with the best and most accredits elements of other sciences, we should not find so many hoary-headed Christians unable to defend their own professed principles, and led astray by the artful votaries of error. That firm and accurate foundation of knowledge which is laid in youth, is most apt to remain unmoved, and to serve as a basis for the loftiest and most useful superstructure in after life.
– Samuel Miller, July 1830; cited in James Garretson’s book, An Able and Faithful Ministry: Samuel Miller and the Pastoral Office.