Which is as a bridegroom coming out of his chamber - That is, when he rises in the morning. He rises from the darkness of the night, and comes forth as the bridegroom comes out of the chamber where he has slept. The allusion is to the bright, and joyful, and cheerful aspect of the rising sun. The image of the bridegroom is employed because we associate with a bridegroom the idea of hilarity, cheerfulness, joy. The essential image is that the sun seems to rise from a night of repose, as man does in the morning, and that after such a night of repose he goes forth with cheerfulness and alacrity to the employments of the day. The figure is an obvious but a very beautiful one, though there is a transition from the image employed in the previous verse, where the sun is represented as dwelling in a tent or tabernacle fitted up for it in the heavens. In the next member of the sentence the figure is again changed, by his being represented as a man prepared to run a race.
And rejoiceth as a strong man to run a race - As a man who is vigorous and powerful, when he enters on a race. He is girded for it; he summons all his strength; he seems to exult in the idea of putting his strength to the test, and starting off on his career. Compare the note at 1-Corinthians 9:24-27. The same comparison which is employed here occurs in the Zendavesta, ii. 106. DeWette. The idea is that the sun seems to have a long journey before him, and puts forth all his vigour, exulting in the opportunity of manifesting that vigour, and confident of triumphing in the race.

Which is as a bridegroom, etc. - This is a reference to the rising of the sun, as the following verse is to the setting. He makes his appearance above the horizon with splendor and majesty; every creature seems to rejoice at his approach; and during the whole of his course, through his whole circuit, his apparent revolution from east to west, and from one tropic to the same again, no part of the earth is deprived of its proper proportion of light and heat. The sun is compared to a bridegroom in his ornaments, because of the glory and splendour of his rays; and to a giant or strong man running a race, because of the power of his light and heat. The apparent motion of the sun, in his diurnal and annual progress, are here both referred to. Yet both of these have been demonstrated to be mere appearances. The sun's diurnal motion arises from the earth's rotation on its axis from west to east in twenty-three hours, fifty-six minutes, and four seconds, the mean or equal time which elapses between the two consecutive meridian-transits of the same fixed star. But on account of the sun's apparent ecliptic motion in the same direction, the earth must make about the three hundred and sixty-fifth part of a second revolution on its axis before any given point of the earth's surface can be again brought into the same direction with the sun as before: so that the length of a natural day is twenty-four hours at a mean rate. The apparent revolution of the sun through the twelve constellations of the zodiac in a sidereal year, is caused by the earth's making one complete revolution in its orbit in the same time. And as the earth's axis makes an angle with the axis of the ecliptic of about twenty-three degrees and twenty eight minutes, and always maintains its parallelism, i.e., is always directed to the same point of the starry firmament; from these circumstances are produced the regular change of the seasons, and continually differing lengths of the days and nights in all parts of the terraqueous globe, except at the poles and on the equator. When we say that the earth's axis is always directed to the same point of the heavens, we mean to be understood only in a general sense; for, owing to a very slow deviation of the terrestrial axis from its parallelism, named the precession of the equinoctial points, which becomes sensible in the lapse of some years, and which did not escape the observation of the ancient astronomers, who clearly perceived that it was occasioned by a slow revolution of the celestial poles around the poles of the ecliptic, the complete revolution of the earth in its orbit is longer than the natural year, or the earth's tropical revolution, by a little more than twenty minutes; so that in twenty-five thousand seven hundred and sixtythree entire terrestrial revolutions round the sun, the seasons will be renewed twenty-five thousand seven hundred and sixty-four times. And in half this period of twelve thousand eight hundred and eighty-two natural years, the points which are now the north and south poles of the heavens, around which the whole starry firmament appears to revolve, will describe circles about the then north and south poles of the heavens, the semi-diameters of which will be upwards of forty-seven degrees.
Coming out of his chamber - מחפתו mechuppatho, from under his veil. It was a sort of canopy erected on four poles, which four Jews held over the bridegroom's head.

Which [is] as a bridegroom coming out of his (e) chamber, [and] rejoiceth as a strong man to run a race.
(e) Or vail. The custom was that the bride and bridegroom would stand under a vail together, and after come forward with great solemnity and rejoicing of the assembly.

Which is as a bridegroom coming out of his chamber,.... His nuptial chamber, on which Elias writes (y),
"we call the garment (or canopy) spread over the head of the bridegroom and bride, supported by four pillars, in the time of their espousals, ''
who looks lovely and beautiful in his nuptial robes, cheerful and pleasant in his countenance, creating pleasure and delight in all his friends that see him and hear his voice: and this simile is expressive of the brightness and glory of the sun when it rises; and of the joy and pleasure which it produces in the minds of men when they behold it: all which sets forth the loveliness and beauty of Christ, as he is held forth in the ministration of the Gospel, and the joy unspeakable and full of glory which his presence yields, after a short departure from his people; see Isaiah 61:10;
and rejoiceth as a strong man to run a race; in which he shows his readiness, velocity, and strength; and this denotes the swiftness of the sun in running its course, and its indefatigableness in its constant motion; though it has been employed therein for so many thousands of years, yet every morning rises with the same cheerfulness, pursues its course, and is never weary: all which may point at the readiness of Gospel ministers, their swiftness to run to and fro, and their strength to fulfil the course of their ministry, in which Christ, the sun of righteousness, is held forth in so glorious a manner.
(y) Elias, in his Tishbi, p. 119. The same word is used Isaiah. iv. 5. and translated "a defence".

The sun, as the most glorious heavenly body, is specially used to illustrate the sentiment; and his vigorous, cheerful, daily, and extensive course, and his reviving heat (including light), well display the wondrous wisdom of his Maker.

Bridegroom - Gloriously adorned with light as with a beautiful garment, and smiling upon the world with a pleasant countenance. Chamber - In which he is poetically supposed to have rested all night, and thence to break forth as it were on a sudden. Strong man - Conscious and confident of his own strength.