A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown [1882] at sacred-texts.com
The trine repetitions are emphatic (compare Psa 118:10-12, Psa 118:15-16; Psa 115:12-13).
Let . . . say--Oh! that Israel may say.
now--as in Psa 115:2; so in Psa 118:3-4. After "now say" supply "give thanks."
that his mercy--or, "for His mercy."
distress--literally, "straits," to which "large place" corresponds, as in Psa 4:1; Psa 31:8.
Men are helpless to hurt him, if God be with him (Psa 56:9), and, if enemies, they will be vanquished (Psa 54:7).
Even the most powerful men are less to be trusted than God.
Though as numerous and irritating as bees [Psa 118:12], by God's help his enemies would be destroyed.
as the fire of thorns--suddenly.
in the name, &c.--by the power (Psa 20:5; Psa 124:8).
The enemy is triumphantly addressed as if present.
rejoicing and salvation--the latter as cause of the former.
right hand . . . is exalted--His power greatly exerted.
He would live, because confident his life would be for God's glory.
Whether an actual or figurative entrance into God's house be meant, the purpose of solemn praise is intimated, in which only the righteous would or could engage.
These words are applied by Christ (Mat 21:42) to Himself, as the foundation of the Church (compare Act 4:11; Eph 2:20; Pe1 2:4, Pe1 2:7). It may here denote God's wondrous exaltation to power and influence of him whom the rulers of the nation despised. Whether (see on Psa 118:1) David or Zerubbabel (compare Hag 2:2; Zac 4:7-10) be primarily meant, there is here typically represented God's more wonderful doings in exalting Christ, crucified as an impostor, to be the Prince and Saviour and Head of His Church.
This is the day--or period distinguished by God's favor of all others.
Save now--Hebrew, "Hosanna" (compare Psa 115:2, &c., as to now) a form of prayer (Psa 20:9), since, in our use, of praise.
he that cometh . . . Lord--As above intimated, this may be applied to the visible head of the Jewish Church entering the sanctuary, as leading the procession; typically it belongs to Him of whom the phrase became an epithet (Mal 3:1; Mat 21:9).
showed us light--or favor (Psa 27:1; Psa 97:11). With the sacrificial victim brought bound to the altar is united the more spiritual offering of praise (Psa 50:14, Psa 50:23), expressed in the terms with which the Psalm opened.