Rashi on TanakhPsalms 20

May the Lord answer you on a day of distress This psalm was [composed] because he [David] would send Joab and all Israel to war, and he would stand in Jerusalem and pray for them, as the matter is stated (in II Sam. 18:3): “It is better that you be for us from the city as aid.” Were it not for David, Joab would not have succeeded in battle.

the name of the God of Jacob Who promised him [Jacob] when he went to Haran and kept His promise; therefore, it is stated: “the God of Jacob.”

from His sanctuary From His Holy Temple, in which He dwells.

your meal offerings...burnt offerings They are the prayers that you pray in battle.

fat Heb. ידשנה, an expression of fat, as (in Deut. 31:20): “and it will eat and be satisfied, and it will become obese (ודשן),” i.e., He will accept them [the prayers] willingly like fat burnt offering.

Let us sing praises for your salvation When the Holy One, blessed be He, saves you, we will all sing praises to the Holy One, blessed be He.

and let us assemble in the name of our God Heb. נדגל, let us assemble and become strong.

Now I know This is the praise that we will sing now for this salvation that came to Joab and to Israel: I know that the Omnipresent desired me and has answered me from His holy heavens, for their salvation is my salvation.

These trust in chariots Some nations trust in their iron chariots, and some trust in horses, but we pray in the name of the Lord, because the salvation is His. נזכיר is an expression of burning sacrifices and of prayer, as (in Isa. 66:3): “he who burns (מזכיר) frankincense,” (and in Lev. 2:2): “its memorial part (אזכרתה).” Therefore, they kneel and fall...

but we rise and gain strength We gain strength over them, as (below 147:6): “strengthens (מעודד) the humble,” an expression of strength.