English Basic Explanation - Chapter 20
This Psalm was composed for situations of warfare, as a prayer offered on behalf of the Israelite combatants. It addresses an individual (or group of individuals) preparing for battle and prays that God should answer the warrior's prayers and grant him victory. Rashi explains that David here speaks to his army before they went to war, on the occasions when he remained behind. Ibn Ezra, by contrast, suggests that somebody else composed this chapter addressing David, expressing his prayers and wishes on the king's behalf as he set out for war.
David (or, according to Ibn Ezra, the person composing this chapter) prays that God should assist the soldier "from the sacred" and "from Zion" (verse 3), referring, of course, to the Beit Ha'mikdash, which is seen as the source of God's blessing and salvation. He then pledges to sing and give praise to the Almighty upon the soldier's triumph (verse 6). Towards the end of the chapter (verses 8-9), David seeks to allay the soldier's fears upon envisioning the enemy's arsenal and sophisticated weaponry. He assures him that the "Name of God" which he represents and carries with him to the battlefield is far more powerful than any manmade ammunition and will assuredly grant him victory.
This chapter ranks among the most familiar Psalms given its inclusion in the daily prayer service. The reason for its inclusion, perhaps, is that this Psalm provides hope and encouragement during times of crisis, assuring us of God's ability to assist even under the direst circumstances. As we all confront difficult situations on one level or another each day, we recite this chapter as an appeal to the Almighty for assistance. Indeed, this Psalm is commonly recited by individuals and communities in times of crisis, Heaven forbid. On festive occasions, such as Shabbat, Rosh Chodesh and holidays, this Psalm is omitted from the prayer service, as the aura of anxiety and tension reflected in this chapter is inconsonant with the joyous and cheerful spirit of these occasions.