Is any among you afflicted? he means that there is no time in which God does not invite us to himself. For afflictions ought to stimulate us to pray; prosperity supplies us with an occasion to praise God. But such is the perverseness of men, that they cannot rejoice without forgetting God, and that when afflicted they are disheartened and driven to despair. We ought, then, to keep within due bounds, so that the joy, which usually makes us to forget God, may induce us to set forth the goodness of God, and that our sorrow may teach us to pray. For he has set the singing of psalms in opposition to profane and unbridled joy; and thus they express their joy who are led, as they ought to be, by prosperity to God.

Is any among you afflicted? - By sickness, bereavement, disappointment, persecutions, loss of health or property. The word used here refers to suffering evil of any kind, (κακοπαθεῖ kakopathei.)
Let him pray - That is, prayer is appropriate to trial. The mind naturally resorts to it, and in every way it is proper. God only can remove the source of sorrow; he can grant unto us "a happy issue out of all our afflictions;" he can make them the means of sanctifying the soul. Compare 2-Chronicles 33:12; Psalm 34:4; Psalm 107:6, Psalm 107:13, Psalm 107:28. It matters not what is the form of the trial, it is a privilege which all have to go to God in prayer. And it is an inestimable privilege. Health fails, friends die, property is lost, disappointments come upon us, danger threatens, death approaches - and to whom shall we go but to God? He ever lives. He never fails us or disappoints us if we trust in him, and his ear is ever open to our cries. This would be a sad world indeed, if it were not for the privilege of prayer. The last resource of millions who suffer - for millions suffer every day - would be taken away, if men were denied the access to the throne of grace. As it is, there is no one so poor that he may not pray; no one so disconsolate and forsaken that he may not find in God a friend; no one so broken-hearted that he is not able to bind up his spirit. One of the designs of affliction is to lead us to the throne of grace; and it is a happy result of trials if we are led by our trials to seek God in prayer.
Is any merry? - The word merry now conveys an idea which is not properly found in the original word here. It refers now, in common usage, to light and noisy pleasure; to that which is jovial; to that which is attended with laughter, or which causes laughter, as a merry jest. In the Scriptures, however, the word properly denotes "cheerful, pleasant, agreeable," and is applied to a state of mind free from trouble - the opposite of affliction - happy, Proverbs 15:13, Proverbs 15:15; Proverbs 17:22; Isaiah 24:7; Luke 15:23-24, Luke 15:29, Luke 15:32. The Greek word used here (εὐθυμεῖ euthumei) means, literally, "to have the mind well" (εῦ eu and θυμὸς thumos;) that is, to have it happy, or free from trouble; to be cheerful.
Let him sing psalms - That is, if anyone is happy; if he is in health, and is prospered; if he has his friends around him, and there is nothing to produce anxiety; if he has the free exercise of conscience and enjoys religion, it is proper to express that in notes of praise. Compare Ephesians 5:19-20. On the meaning of the word here rendered "sing psalms," see the notes at Ephesians 5:19, where it is rendered "making melody." It does not mean to sing psalms in contradistinction from singing hymns, but the reference is to any songs of praise. Praise is appropriate to such a state of mind. The heart naturally gives utterance to its emotions in songs of thanksgiving. The sentiment in this verse is well expressed in the beautiful stanza:
In every joy that crowns my days,
In every pain I bear,
My heart shall find delight in praise,
Or seek relief in prayer.
- Mrs. Williams.

Is any among you afflicted? let him pray - The Jews taught that the meaning of the ordinance, Leviticus 13:45, which required the leper to cry, Unclean! unclean! was, "that thus making known his calamity, the people might be led to offer up prayers to God in his behalf," Sota, page 685, ed. Wagens. They taught also, that when any sickness or affliction entered a family, they should go to the wise men, and implore their prayers. Bava bathra, fol. 116, 1.
In Nedarim, fol. 40, 1, we have this relation: "Rabba, as often as he fell sick, forbade his domestics to mention it for the first day; if he did not then begin to get well, he told his family to go and publish it in the highways, that they who hated him might rejoice, and they that loved him might intercede with God for him."
Is any merry? let him sing psalms - These are all general but very useful directions. It is natural for a man to sing when he is cheerful and happy. Now no subject can be more noble than that which is Divine: and as God alone is the author of all that good which makes a man happy, then his praise should be the subject of the song of him who is merry. But where persons rejoice in iniquity, and not in the truth, God and sacred things can never be the subject of their song.

(8) Is any among you afflicted? let him pray. Is any merry? let him sing psalms.
(8) He shows the best remedy against all afflictions, that is, prayers which have their place both in sorrow and joy.

Is any among you afflicted?.... As the people of God generally are; they are commonly a poor, and an afflicted people; at least there are many among them that are so, and many are their afflictions: those whom Christ loves, as he did Lazarus, are not free from sicknesses and diseases; and these are rather signs of love than arguments against it; and when this is the case of any of the saints, what is to be done?
let him pray; to God that can save him; in the name of Christ; under the influence of the Spirit; believing in the word of promise. Times of afflictions are proper times for prayer; there is then more especially need of it; and God sometimes lays his afflicting hand upon his people, when they have been negligent of their duty, and he has not heard of them for some time, in order to bring them near to him, to seek his face, pay him a visit, and pour out a prayer before him; see Psalm 50:15.
Is any merry? in good heart and spirit, in a good frame of mind, as well as in prosperous circumstances, in soul, body and estate:
let him sing psalms; let him not only be inwardly joyful, as he should be in prosperity, and be thankful to God for his many mercies, temporal and spiritual, he enjoys; but let him express it vocally, and melodiously, by singing psalms, hymns, and spiritual songs: not that these are the only persons that are to sing psalms, or this the only time, any more than that afflicted persons are the only ones that are to pray, or the time of affliction the only time of prayer; but as affliction more especially calls for prayer, so spiritual joy, and rejoicing in prosperous seasons, for singing of psalms: weeping, and singing of psalms, were thought, by the Jews, inconsistent. Kimchi, on the title of the third psalm, observes, that their Rabbins say, that when David went up the ascent of the Mount of Olives, he wept; and if he wept, why is this called a psalm? and if a psalm, , "why did he weep?"

afflicted--referring to the "suffering affliction" (James 5:10).
let him pray--not "swear" in rash impatience.
merry--joyous in mind.
sing psalms--of praise. Paul and Silas sang psalms even in affliction.