1. It is here supposed that God alone is the felicity and chief good of man. He, and he only, that made the soul, can make it happy; there is none in heaven, none in earth, that can pretend to do it besides.
2. Here are expressed the workings and breathings of a soul towards God accordingly. If God be our felicity,
(1.) Then we must have him (Whom have I but thee?), we must choose him, and make sure to ourselves an interest in him. What will it avail us that he is the felicity of souls if he be not the felicity of our souls, and if we do not by a lively faith make him ours, by joining ourselves to him in an everlasting covenant?
(2.) Then our desire must be towards him and our delight in him (the word signifies both); we must delight in what we have of God and desire what we yet further hope for. Our desires must not only be offered up to God, but they must all terminate in him, desiring nothing more than God, but still more and more of him. This includes all our prayers, Lord, give us thyself; as that includes all the promises, I will be to them a God. The desire of our souls is to thy name.
(3.) We must prefer him in our choice and desire before any other. [1.] "There is none in heaven but thee, none to seek to or trust in, none to court or covet acquaintance with, but thee." God is in himself more glorious than any celestial being (Ps 89 6), and must be, in our eyes, infinitely more desirable. Excellent beings there are in heaven, but God alone can make us happy. His favour is infinitely more to us than the refreshment of the dews of heaven or the benign influence of the stars of heaven, more than the friendship of the saints in heaven or the good offices of the angels there. [2.] I desire none on earth besides thee; not only none in heaven, a place at a distance, which we have but little acquaintance with, but none on earth neither, where we have many friends and where much of our present interest and concern lie. "Earth carries away the desires of most men, and yet I have none on earth, no persons, no things, no possessions, no delights, that I desire besides thee or with thee, in comparison or competition with thee." We must desire nothing besides God but what we desire for him (nil præter te nisi propter te—nothing besides thee except for thy sake), nothing but what we desire from him, and can be content without so that it be made up in him. We must desire nothing besides God as needful to be a partner with him in making us happy.
(4.) Then we must repose ourselves in God with an entire satisfaction, v. 26. Observe here, [1.] Great distress and trouble supposed: My flesh and my heart fail. Note, Others have experienced and we must expect, the failing both of flesh and heart. The body will fail by sickness, age, and death; and that which touches the bone and the flesh touches us in a tender part, that part of ourselves which we have been but too fond of; when the flesh fails the heart is ready to fail too; the conduct, courage, and comfort fail. [2.] Sovereign relief provided in this distress: But God is the strength of my heart and my portion for ever. Note, Gracious souls, in their greatest distresses, rest upon God as their spiritual strength and their eternal portion. First, "He is the strength of my heart, the rock of my heart, a firm foundation, which will bear my weight and not sink under it. God is the strength of my heart; I have found him so; I do so still, and hope ever to find him so." In the distress supposed, he had put the case of a double failure, both flesh and heart fail; but, in the relief, he fastens on a single support: he leaves out the flesh and the consideration of that, it is enough that God is the strength of his heart. He speaks as one careless of the body (let that fail, there is no remedy), but as one concerned about the soul, to be strengthened in the inner man. Secondly, "He is my portion for ever; he will not only support me while I am here, but make me happy when I go hence." The saints choose God for their portion, they have him for their portion, and it is their happiness that he will be their portion, a portion that will last as long as the immortal soul lasts.
Excerpts taken from Matthew Henry's Commentary on the Whole Bible