First. It is the duty of Christians to be settled in the doctrine of faith. It is the apostle’s prayer, 1 Pet. v. 10, “The God of all grace stablish, strengthen, settle you.” That is, that they might not be meteors in the air, but fixed stars. . . . Now, such as are not settled in religion, will, at one time or other, prove wandering stars; they will lose their former steadfastness, and wander from one opinion to another. Such as are unsettled are the tribe of Reuben “unstable as water,” Gen. xlix. 4; like a ship without ballast, overturned with every wind of doctrine. Beza writes of one Belfectius, that his religion changed as the moon. The Arians had every year a new faith. These are not pillars in the temple of God, but reeds shaken every way. The apostle calls them “damnable heresies.” 2 Pet. ii. 1. A man may go to hell as well for heresy as adultery. To be unsettled in religion, argues want of judgment. If their heads were not giddy, men would not reel so fast from one opinion to another. It argues lightness. As feathers will be blown every way, so will feathery Christians. . . . Therefore such are compared to children. Eph. iv. 14. “That we be no more children, tossed to an fro.” Children are fickle, sometimes of one mind, sometimes of another, nothing pleases them long; so unsettled Christians are childish; the truths they embrace at one time, they reject at another; sometimes they like the Protestant religion, and soon after they have a good mind to turn to Papists.
[One of the solutions: the preaching of the Word]
It is the great end of the word preached, to bring us to a settlement in religion. Eph. iv. 11, 12, 14. “And he gave some, evangelists; and some, pastors and teachers; for the edifying of the body of Christ; that we henceforth be no more children.” The word is called a hammer. Jer. xxiii. 29. Every blow of the hammer is to fasten the nails of the building; so the preacher’s words are to fasten you the more to Christ; they weaken themselves to strengthen and settle you. This is the grand design of preaching, not only for the enlightening, but for the establishing of souls; not only to guide them in the right way, but to keep them in it. Now, if you be not settled, you do not answer God’s end in giving you the ministry (A Body of Divinity, pp. 1-2).