For whosoever are led by the Spirit of God, etc. This is a confirmation of what has immediately preceded; for he teaches us, that those only are deemed the sons of God who are ruled by his Spirit; for by this mark God acknowledges them as his own people. Thus the empty boasting of hypocrites is taken away, who without any reason assume the title; and the faithful are thus encouraged with unhesitating confidence to expect salvation. The import of the whole is this -- "all those are the sons of God who are led [1] by God's Spirit; all the sons of God are heirs of eternal life: then all who are led by God's Spirit ought to feel assured of eternal life. But the middle term or assumption is omitted, for it was indubitable. But it is right to observe, that the working of the Spirit is various: for there is that which is universal, by which all creatures are sustained and preserved; there is that also which is peculiar to men, and varying in its character: but what he means here is sanctification, with which the Lord favors none but his own elect, and by which he separates them for sons to himself.

Footnotes

1 - Agontai -- are led or conducted: "A metaphor taken from the blind or those in darkness, who know not how to proceed without a conductor. So we have need to be led by the Spirit in the way of truth, for we are blind and see no light. Or it is a metaphor taken from infants, who can hardly walk without a guide; for the regenerated are like little children lately born. Thus we are reminded of our misery and weakness; and we ought not to ascribe to ourselves either knowledge or strength apart from the Spirit of God." -- Pareus

For as many - Whosoever; all who are thus led. This introduces a new topic, illustrating the benefits of the gospel, to wit, that it produces a spirit of adoption, Romans 8:14-17.
As are led - As submit to his influence and control. The Spirit is represented as influencing, suggesting, and controlling. One evidence of piety is, a willingness to yield to that influence, and submit to him. One decided evidence of the lack of piety is, where there is an unwillingness to submit to that influence, but where the Holy Spirit is grieved and resisted. All Christians submit to his influence; all sinners decidedly reject it and oppose it. The influence of the Spirit, if followed, would lead every man to heaven. But when neglected, rejected, or despised, man goes down to hell. The glory belongs to the conducting Spirit when man is saved; the fault is man's when he is lost. The apostle here does not agitate the question how it is that the people of God are led by the Spirit, or why they yield to it when others resist it. His design is simply to state the fact, that they who are thus led are the sons of God, or have evidence of piety.
Are the sons of God - Are adopted into his family, and are his children. This is a name of endearment, meaning that they sustain to him this relation; that they are his friends, disciples, and imitators; that they are parts of the great family of the redeemed, of whom he is the Father and Protector. It is often applied to Christians in the Bible; Job 1:6; John 1:12; Philippians 2:15; 1-John 3:1-2; Matthew 5:9, Matthew 5:45; Luke 6:35. This is a test of piety which is easily applied.
(1) are we conscious that an influence from above has been drawing us away from the corrupting passions and vanities of this world? This is the work of the Spirit.
(2) are we conscious of a desire to yield to that influence, and to be conducted in the path of purity and life? This is an evidence that we are the sons of God.
(3) do we offer no resistance; do we follow cheerfully, and obey this pure influence, leading us to mortify pride, subdue passion, destroy lust, humble ambition, and annihilate the love of wealth and of the world? If so, we are his children. God will not lead us astray; and our peace and happiness consists only in yielding ourselves to this influence entirely, and in being willing to be conducted by this unseen hand "beside the still waters of salvation."

For as many as are led by the Spirit, etc. - No man who has not Divine assistance can either find the way to heaven, or walk in it when found. As Christ, by his sacrificial offering, has opened the kingdom of God to all believers; and, as a mediator, transacts the concerns of their kingdom before the throne; so the Spirit of God is the great agent here below, to enlighten, quicken, strengthen, and guide the true disciples of Christ; and all that are born of this Spirit are led and guided by it; and none can pretend to be the children of God who are not thus guided.

(16) For as many as are led by the Spirit of God, they are the sons of God.
(16) A confirmation of this reason: for they are the children of God who are governed by his Spirit, therefore they will have everlasting life.

For as many as are led by the Spirit of God,.... Not by the spirit of the world, or of the devil, or by their own spirits: the act of leading ascribed to the Spirit is either in allusion to the leading of blind persons, or such who are in the dark; or rather to the leading of children and teaching them to go; which supposes life in those that are led, and some degree of strength, though a good deal of weakness; and is a display of powerful and efficacious grace, and is always for their good: the Spirit of God leads them from sin, and from a dependence on their own righteousness, in paths they formerly knew not, and in which they should go, in the paths of faith and truth, of righteousness and holiness, and in a right, though sometimes a rough way; he leads them to the person, blood, and righteousness of Christ, and to the fulness of grace in him; into the presence of God, to the house and ordinances of God; into the truths of the Gospel, from one degree of grace to another, and at last to glory; which he does gradually, by little and little he leads them to see the iniquity of their hearts and natures, to lay hold on Christ and salvation by him, into the doctrines of grace, and the love and favour of God, and proportionally to the strength he gives: now such persons,
they are the sons of God: not in so high a sense as Christ is; nor in so low a sense as Adam was, and angels are; much less in such sense as wicked magistrates be; nor merely as professors of religion in common; but by adoption, not national, such as that of the Jews, but special; and which has some agreement with civil adoption, it being of persons to an inheritance, which they have no legal right unto, and it is done freely: though there is a difference between the one and the other; for in divine adoption there is no need on the adopter's side; nor no worth on the side of the adopted; proper qualifications are conveyed to them for the enjoyment of the inheritance, and which is enjoyed, the father and firstborn being living, and is an inheritance which vastly exceeds all others: now this blessing of being the sons of God, is owing not to ourselves, nor to our earthly parents, but to God; to the Father, who predestinated to it, and fixed it in the covenant of grace; to Christ, it is by him, as the Son of God, it is through him, as the Mediator, and it is for him, it is for his glory; and also to the Spirit of God, who manifests it, works faith to receive it, witnesses to it, and seals up to the full enjoyment of it. This favour is an instance of surprising grace, exceeds other blessings, makes the saints honorourable, is attended with many privileges, and lasts for ever: such who are in this relation to God, ought to ascribe it to his grace, to require him with thankfulness, and a becoming conversation, to be followers of him, and to love, honour, and obey him.

For as many as are led by the Spirit of God, they are the sons of God, they, &c.--"these are sons of God." Hitherto the apostle has spoken of the Spirit simply as a power through which believers mortify sin: now he speaks of Him as a gracious, loving Guide, whose "leading"--enjoyed by all in whom is the Spirit of God's dear Son--shows that they also are "sons of God."

For as many as are led by the Spirit of God - In all the ways of righteousness. They are the sons of God - Here St. Paul enters upon the description of those blessings which he comprises, Romans 8:30, in the word glorified; though, indeed, he does not describe mere glory, but that which is still mingled with the cross. The sum is, through sufferings to glory.