This psalm is obviously divided into two parts, but there is no reason for seeing in these two originally unconnected fragments. Rather does each part derive force from the other; and nothing is more natural than that, after the congregation has spoken its joyful summons to itself to worship, Jehovah should speak warning words as to the requisite heart-preparation, without which worship is vain. The supposed fragments are fragmentary indeed, if considered apart. Surely a singer has the liberty of being abrupt and of suddenly changing his tone. Surely he may as well be credited with discerning the harmony of the change of key as some later compiler. There could be no more impressive way of teaching the conditions of acceptable worship than to set side by side a glad call to praise and a solemn warning against repeating the rebellions of the wilderness. These would be still more appropriate if this were a post-exilic hymn; for the second return from captivity would be felt to be the analogue of the first, and the dark story of former hard-heartedness would fit very close to present circumstances. The invocation to praise in vv. 1, 2, gives a striking picture of the joyful tumult of the Temple worship. Shrill cries of gladness, loud shouts of praise, songs with musical accompaniments, rang simultaneously through the courts, and to Western ears would have sounded as din rather than as music, and as more exuberant than reverent. The spirit expressed is, alas! almost as strange to many moderns as the manner of its expression. That swelling joy which throbs in the summons, that consciousness that jubilation is a conspicuous element in worship, that effort to rise to a height of joyful emotion, are very foreign to much of our worship. And their absence, or presence only in minute amount, flattens much devotion, and robs the Church of one of its chief treasures. No doubt, there must often be sad strains blended with praise. But it is a part of Christian duty, and certainly of Christian wisdom, to try to catch that tone of joy in worship which rings in this psalm.