[The following excerpt is taken from The Fountain of Life, a book by the Puritan John Flavel. I read this after having a conversation with a friend about the necessity of thinking through difficult theological issues. I was greatly encouraged by this; I hope you are, too.]
The knowledge of Jesus Christ is a fundamental knowledge; and foundations are most useful, though least seen.
It is fundamental to all graces; they all begin in knowledge. The new man is “renewed in knowledge.” Col 3:10. As the old, so the new creation begins in light; the opening of the eyes is the first work of the Spirit: and as the beginnings of grace, so all its growth depends upon this increasing knowledge: “But grow in grace, and in the knowledge of our Lord and Saviour.” 2Pet. 3:18. See how these two, grace and knowledge, keep equal pace in the soul of the Christian; in what degree the one increases, the other increases also.
It is fundamental to all duties. The duties as well as the graces of all Christians, are all founded in the knowledge of Christ. Must a Christian believe? That he can never do without the knowledge of Christ: faith is so much dependent upon his knowledge, that it is denominated by it, “By his knowledge shall my righteous servant justify many,” Isa. 53:11; and hence, John 6:40, seeing and believing are made the same thing. Would a man exercise hope in God? That he can never do without the knowledge of Christ, for he is the author of that hope, 1 Pet. 1:3; he is also its object, Heb. 6:19, its groundwork and support, Col. 1:27. As you cannot believe or hope, so neither can you pray acceptably without a competent degree of this knowledge. The very heathen could say, “Men must not speak of God without light.” The true way of conversing with, and enjoying God in prayer, is by acting in faith on him through a Mediator. Oh, then, how indispensible is the knowledge of Christ to all who address themselves to God in any duty.
It is fundamental to all comforts: all the comforts of believers are streams from this fountain. Jesus Christ is the very object of a believer’s joy: “We rejoice in Christ Jesus.” Phil. 3:3. Take away the knowledge of Christ, and Christians would be the most sad and melancholy beings in the world: again, let Christ but manifest himself, and dart the beams of his light into their souls, it will make them kiss the stake, sing in the flames, and shout in the pangs of death, as men that divide the spoil.
This knowledge is fundamental to the eternal happiness of souls: as we can perform no duty, enjoy no comfort, so neither can we be saved without it. “This is life eternal, that they might know thee the only true God, and Jesus Christ whom thou hast sent.” John 17:3. And if it be life eternal to know Christ, then it is eternal damnation to be ignorant of Christ: as Christ is the door that opens heaven, so knowledge is the key that opens Christ. The excellent gifts and renowned parts of the moral heathen, though they purchased them to great esteem and honor among men, yet left them in a state of perdition, because of this great defect, that they were ignorant of Christ. 1 Cor. 1:21.