The Hebrew Psalter numbers 150 songs. The corresponding number in the LXX differs because of a different division of certain psalms. Hence the numbering in the Greek Psalter (which was followed by the Latin Vulgate) is usually one digit behind the Hebrew. In the New American Bible the numbering of the verses follows the Hebrew numbering; many of the traditional English translations are often a verse number behind the Hebrew because they do not count the superscriptions as a verse.
The superscriptions derive from pre-Christian Jewish tradition, and they contain technical terms, many of them apparently liturgical, which are no longer known to us. Seventy-three psalms are attributed to David, but there is no sure way of dating any psalm. Some are pre-exilic (before 587), and others are post-exilic (after 539), but not as late as the Maccabean period (ca. 165). The psalms are the product of many individual collections (e.g., Songs of Ascents, Psa 120-134), which were eventually combined into the present work in which one can detect five “books,” because of the doxologies which occur at ⇒ 41:14; ⇒ 72:18-19; ⇒89:53; ⇒ 106:48.
Two important features of the psalms deserve special notice. First, the majority were composed originally precisely for liturgical worship. This is shown by the frequent indication of liturgical leaders interacting with the community (e.g., ⇒ Psalm 118:1-4). Secondly, they follow certain distinct patterns or literary forms. Thus, the hymn is a song of praise, in which a community is urged joyfully to sing out the praise of God. Various reasons are given for this praise (often introduced by “for” or “because”): the divine work of creation and sustenance (⇒ Psalm 135:1-12; 136). Some of the hymns have received a more specific classification, based on content. The “Songs of Zion” are so called because the exalt Zion, the city in which God dwells among the people (Psalm 47:96-99). Characteristic of the songs of praise is the joyful summons to get involved in the activity; Psa 104 is an exception to this, although it remains universal in its thrust.
Another type of psalm is similar to the hymn: the thanksgiving psalm. This too is a song of praise acknowledging the Lord as the rescuer of the psalmist from a desperate situation. Very often the psalmist will give a flash-back, recounting the past distress, and the plea that was uttered (Psa 30; 116). The setting for such prayers seems to have been the offering of a todah (a “praise” sacrifice) with friends in the Temple.
There are more psalms of lament than of any other type. They may be individual (e.g., Psa 3-7; 22) or communal (e.g., Psa 44). Although they usually begin with a cry for help, they develop in various ways. The description of the distress is couched in the broad imagery typical of the Bible (one is in Sheol, the Pit, or is afflicted by enemies or wild beasts, etc.) – in such a way that one cannot pinpoint the exact nature of the psalmist’s plight. However, Psa 51 (cf also Psa 130) seems to refer clearly to deliverance from sin. Several laments end on a note of certainty that the Lord has heard the prayer (cf. Psa 7, but contrast Psa 88), and the Psalter has been characterized as a movement from lament to praise. If this is somewhat of an exaggeration, it serves at least to emphasize the frequent expressions of trust which characterize the lament. In some cases it would seem as if the theme of trust has been lifted out to form a literary type all its own; cf. Psa 23, 62, 91. Among the communal laments can be counted Psa 74 and 79. They complain to the Lord about some national disaster, and try to motivate God to intervene in favor of the suffering people.
Other psalms are clearly classified on account of content, and they may be in themselves laments or psalms of thanksgiving. Among the “royal: psalms, that deal directly with the currently reigning king, are Psa 20, 21, and 72. Many of the royal psalms were given a messianic interpretation by Christians. In Jewish tradition they were preserved, even after kingship had disappeared, because they were read in the light of the Davidic covenant reported in 2 Samuel 7. Certain psalms are called wisdom psalms because they seem to betray the influence of the concerns of the ages (cf. Psa 37,49), but there is no general agreement as to the number of these prayers. Somewhat related to the wisdom psalms are the “torah” psalms, in which the torah (instruction or law) of the Lord is glorified (Psa 1; ⇒ 19:8-14; 119). Psa 78, 105, 106 can be considered as “historical” psalms. Although the majority of the psalms have a liturgical setting, there are certain prayers that may be termed “liturgies,” so clearly does their structure reflect a liturgical incident (e.g., Psa 15, 24).
It is obvious that not all of the psalms can be pigeon-holed into neat classifications, but even a brief sketch of these types help us to catch the structure and spirit of the psalms we read. It has been rightly said that the psalms are “a school of prayer.” They not only provide us with models to follow, but inspire us to voice our own deepest feelings and aspirations.