Romans 8:29

For whom he did foreknow
The foreknowledge of God here, does not intend his prescience of all things future; by which he foreknows and foretells things to come, and which distinguishes him from all other gods; and is so called, not with respect to himself, with whom all things are present, but with respect to us, and which is eternal, universal, certain, and infallible; for in this sense he foreknows all men, and if this was the meaning here, then all men would be predestinated, conformed to the image of Christ, called by grace, justified and glorified; whereas they are a special people, whom God has foreknown: nor is this foreknowledge to be understood of any provision or foresight of the good works, holiness, faith, and perseverance of men therein, upon which God predestinates them to happiness; since this would make something out of God, and not his good pleasure, the cause of predestination; which was done before, and without any consideration of good or evil, and is entirely owing to the free grace of God, and is the ground and foundation of good works, faith, holiness, and perseverance in them: but this regards the everlasting love of God to his own people, his delight in them, and approbation of them; in this sense he knew them, he foreknew them from everlasting, affectionately loved them, and took infinite delight and pleasure in them; and this is the foundation of their predestination and election, of their conformity to Christ, of their calling, justification, and glorification: for these

he also did predestinate to be conformed to the image of his Son;
having perfect, distinct, special knowledge of them, joined with love to them, he predetermined, or fore-appointed them in his eternal mind, in his everlasting and unchangeable purposes and decrees to this end, conformity to the image of Christ; which is not to be understood of the Spirit of Christ: God's elect indeed are chosen to be holy, and through sanctification of the Spirit, but are never said to be conformed, made like to the Spirit, nor is the Spirit ever called the image of Christ; but this designs either likeness to Christ as the Son of God, or conformity to him in his human nature. There is indeed a great disparity between the sonship of Christ, and of the saints; he is the eternal and natural Son of God, he is the one and only begotten Son, they are adopted ones, yet in some things there is a likeness; as he is the Son of God, so are they the sons of God, though not in the same sense; as he is a beloved Son, so are they; as he is the firstborn with respect them, they are the firstborn with respect to angels; as he has an inheritance, so have they; moreover, he has a very great concern in their sonship; the predestination of them to it is by him; the blessing itself is founded on union to him, on their conjugal relation to him, and his assumption of their nature; it comes to them through his redemption, and is actually bestowed on them by him; and this conformity to Christ as sons, will mere fully appear hereafter, when they shall be like him, and see him as he is: or this may be understood of the saints' conformity to Christ in his human nature, both here and hereafter: here in holiness; the image of God was in in his first creation, this is defaced by sin; and in regeneration, the image of Christ is stamped, his grace is wrought in them, his Spirit is put into them, to enable them to walk in him, and after him: this will be complete hereafter, and will consist in perfect holiness, being freed from the very being, as well as the power and guilt of sin; in perfect knowledge of everything that will tend to their happiness; and in glory like to Christ, both in soul and body:

that he might be the firstborn among many brethren;
the persons among whom Christ is the firstborn are described by their relation, "brethren"; to one another, being related to the same Father, regenerated by the same grace, taken into the same family, and heirs of the same glory; and to Christ, which relation, as brethren to him, is not merely founded on his incarnation, but in their adoption; and which is evidenced by their regeneration, and doing the will of his Father; an which relation he owns, and is not ashamed of: they are also described by their number, "many"; for though they are but few, when compared with the world; yet they are many, a large number, considered by themselves; and among these, Christ is the "firstborn"; he is the firstborn of God, the begotten of the Father, he is the first begotten, and as such he is the only begotten; he is the firstborn of Mary, she had none before him, and he is the only one that ever was born in the manner he was; he is the first begotten from the dead, his resurrection is called a begetting, and he was the first in time that rose from the dead by his own power, and to an immortal life, and the first in causality and dignity. Christ is the firstborn with respect to all creatures in general; he was begotten of the Father before all creatures were; he is the first cause of them all, the governor, basis, and support of them: and he is the firstborn with respect to the saints; who are of the same nature with him, are made partakers of the divine nature, are sons in the same family, though not in the same class of sonship: moreover, this character may regard not so much birth as privilege which belongs to Christ as Mediator; who, as the firstborn had, has the blessing, the government, the priesthood, and the inheritance; all which is owing to, and is one end of divine predestination. The Cabalistic ^F13 writers among the Jews give the name of "firstborn" to the second Sephira, number, or person, "Wisdom", which answers to the Son of God.