But he who searches hearts, etc. This is a remarkable reason for strengthening our confidence, that we are heard by God when we pray through his Spirit, for he thoroughly knows our desires, even as the thoughts of his own Spirit. And here must be noticed the suitableness of the word to know; for it intimates that God regards not these emotions of the Spirit as new and strange, or that he rejects them as unreasonable, but that he allows them, and at the same time kindly accepts them, as allowed and approved by him. As then Paul had before testified, that God then aids us when he draws us as it were into his own bosom, so now he adds another consolation, that our prayers, of which he is the director, shall by no means be disappointed. The reason also is immediately added, because he thus conforms us to his own will. It hence follows, that in vain can never be what is agreeable to his will, by which all things are ruled. Let us also hence learn, that what holds the first place in prayer is consent with the will of the Lord, whom our wishes do by no means hold under obligation. If then we would have our prayers to be acceptable to God, we must pray that he may regulate them according to his will.

And he that searcheth the hearts - God. To search the heart is one of his attributes which cannot be communicated to a creature; Jeremiah 17:10.
Knoweth what is the mind of the Spirit - Knows the desires which the Holy Spirit excites and produces in the heart. He does not need that those deep emotions should be expressed in words; he does not need the eloquence of language to induce him to hear; but he sees the anxious feelings of the soul, and is ready to aid and to bless.
Maketh intercession for the saints - Aids and directs Christians.
According to the will of God - Greek, "According to God." It is according to his will in the following respects:
(1) The Spirit is given according to his will. It is his gracious purpose to grant his aid to all who truly love him.
(2) the desires which he excites in the heart of the Christian are those which are according to his will; they are such as God wishes to exist; the contrite, humble, and penitent pleading of sinners for mercy.
(3) he superintends and guards Christians in their prayers.
It is not meant that they are infallible, or that they never make an improper petition, or have an improper desire; but that he has a general superintendence over their minds, and that so far as they will yield themselves to his direction, they shall not be led into error That man is most safe who yields himself most entirely to the influence of the Holy Spirit. And the doctrine here stated is one that is full of consolation to the Christian. We are poor, and needy, and ignorant, and blind; we are the creatures of a day, and are crushed before the moth. But in the midst of our feebleness we may look to God for the aid of his Spirit, and rejoice in his presence, and in his power to sustain us in our sighings, and to guide us in our wanderings.

He maketh intercession for the saints - The word εντυγχανω signifies to apply one's self to a person in behalf of another; to intercede or negotiate for. Our Lord makes intercession for us, by negotiating and managing, as our friend and agent, all the affairs pertaining to our salvation. And the Spirit of God makes intercession for the saints, not by supplication to God on their behalf, but by directing and qualifying their supplications in a proper manner, by his agency and influence upon their hearts; which, according to the Gospel scheme, is the peculiar work and office of the Holy Spirit. See Taylor.
According to the will of God - Κατα Θεον· According to the mind, intention, or design of God. And thus the prayers which we offer up, and the desires which subsist in the unutterable groanings, are all such as are pleasing in the sight of God. So that God, whose is the Spirit, and who is acquainted with the mind of the Spirit, knows what he means when he leads the saints to express themselves in words, desires, groans, sighs, or tears: in each God reads the language of the Holy Ghost, and prepares the answer according to the request.
From all this we learn that a fluency in prayer is not essential to praying: a man may pray most powerfully in the estimation of God, who is not able to utter even one word. The unutterable groan is big with meaning, and God understands it, because it contains the language of his own Spirit. Some desires are too mighty to be expressed; there is no language expressive enough to give them proper form and distinct vocal sound: such desires show that they came from God; and as they came from him, so they express what God is disposed to do, and what he has purposed to do. This is a matter of great encouragement to all those who are agonizing to enter in at the strait gate.

And he that searcheth the hearts knoweth what [is] the (i) mind of the Spirit, because he maketh intercession for the saints (k) according to [the will of] God.
(i) What sighs and sobs proceed from the impulse of his Spirit.
(k) Because he teaches the godly to pray according to God's will.

And he that searcheth the hearts,.... This is peculiar to God, and a "periphrasis" of him; angels, neither good nor bad, can search into the hearts of men; one man cannot know the heart of another, nor any man fully know his own; this is the prerogative of God: and
he knoweth what is the mind of the Spirit; not the spirit of men, but of God: that affectionate desire and meaning of the Spirit of God, in the unalterable groans of the saints; he knows the wise meaning there is in them, for so may signify, and is opposed to the carnal mind, or wisdom of the flesh, which desires foolish things. The searcher of hearts knows this, not barely by his omniscience, but he regards it, approves of it, attends, and gives an answer to it; which is no small encouragement to pray, though it be but with sighs and groans unutterable; since the omniscient God understands, and respects such kind of prayer: and the reason is,
because he, the Spirit of God,
maketh intercession for the saints, according to the will of God; the persons for whom he intercedes are saints: to whom Christ is made sanctification; who are called to be saints; are sanctified by the Spirit of God, and walk after him: now such are the objects of God's delight, they are chosen by him, preserved in Christ, and have his righteousness imputed to them; to these he has made known his Gospel, has given his grace, and will at last the inheritance; so that intercession made for such will certainly be regarded: it may be rendered, "he maketh intercession for holy things according to God"; for spiritual blessings, divine favours, things that belong to God; or divine things, which are agreeably to his nature and will: and since it is the Holy Spirit that makes intercession, and the persons are holy for whom he makes it, and this is made for holy things, and all according to the will of God, which the Spirit of God must fully know, saints may be confident of the prevalence and success of such intercession.

And--rather, "But," inarticulate though these groanings be.
he that searcheth the hearts knoweth what is the mind of the Spirit, because he--the Spirit
maketh intercession for the saints according to the will of God--As the Searcher of hearts, He watches the surging emotions of them in prayer, and knows perfectly what the Spirit means by the groanings which He draws forth within us, because that blessed Intercessor pleads by them only for what God Himself designs to bestow.
Note, (1) Are believers "led by the Spirit of God" (Romans 8:14)? How careful then should they be not to "grieve the Holy Spirit of God" (Ephesians 4:30)! Compare Psalm 32:8-9 : "I will . . . guide thee with Mine eye. Be not (then) as the horse, or as the mule," &c. (2) "The spirit of bondage," to which many Protestants are "all their lifetime subject," and the "doubtsome faith" which the Popish Church systematically inculcates, are both rebuked here, being in direct and painful contrast to that "spirit of adoption," and that witness of the Spirit, along with our own spirit, to the fact of our sonship, which it is here said the children of God, as such, enjoy (Romans 8:15-16). (3) As suffering with Christ is the ordained preparation for participating in this glory, so the insignificance of the one as compared with the other cannot fail to lighten the sense of it, however bitter and protracted (Romans 8:17-18). (4) It cannot but swell the heart of every intelligent Christian to think that if external nature has been mysteriously affected for evil by the fall of man, it only awaits his completed recovery, at the resurrection, to experience a corresponding emancipation from its blighted condition into undecaying life and unfading beauty (Romans 8:19-23). (5) It is not when believers, through sinful "quenching of the Spirit," have the fewest and faintest glimpses of heaven, that they sigh most fervently to be there; but, on the contrary, when through the unobstructed working of the Spirit in their hearts, "the first-fruits" of the glory to be revealed are most largely and frequently tasted, then, and just for that reason, is it that they "groan within themselves" for full redemption (Romans 8:23). For thus they reason: If such be the drops, what will the ocean be? If thus "to see through a glass darkly" be so very sweet, what will it be to "see face to face?" If when "my Beloved stands behind our wall, looking forth at the windows, showing Himself through the lattice" (Song 2:9) --that thin veil which parts the seen from the unseen--if He is even thus to me "Fairer than the children of men," what shall He be when He stands confessed before my undazzled vision, the Only-begotten of the Father in my own nature, and I shall be like Him, for I shall see Him as He is? (6) "The patience of hope" (1-Thessalonians 1:3) is the fitting attitude for those who with the joyful consciousness that they are already "saved" (2-Timothy 1:9; Titus 3:5), have yet the painful consciousness that they are saved but in part: or, "that being justified by His grace, they are made (in the present state) heirs according to the hope (only) of eternal life," Titus 3:7 (Romans 8:24-25). (7) As prayer is the breath of the spiritual life, and the believer's only effectual relief under the "infirmity" which attaches to his whole condition here below, how cheering is it to be assured that the blessed Spirit, cognizant of it all, comes in aid of it all; and in particular, that when believers, unable to articulate their case before God, can at times do nothing but lie "groaning" before the Lord, these inarticulate groanings are the Spirit's own vehicle for conveying into "the ears of the Lord of Sabaoth" their whole case; and come up before the Hearer of prayer as the Spirit's own intercession in their behalf, and that they are recognized by Him that sitteth on the Throne, as embodying only what His own "will" determined before to bestow upon them (Romans 8:26-27)! (8) What a view do these two verses (Romans 8:26-27) give of the relations subsisting between the Divine Persons in the economy of redemption, and the harmony of their respective operations in the case of each of the redeemed!
THIRD: Triumphant Summary of the Whole Argument (Romans 8:28-39).

But he who searcheth the hearts - Wherein the Spirit dwells and intercedes. Knoweth - Though man cannot utter it. What is the mind of the Spirit, for he maketh intercession for the saints - Who are near to God. According to God - According to his will, as is worthy of God. and acceptable to him.