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
Psalms Chapter 50
In the grandeur and solemnity of a divine judgment, God is introduced as instructing men in the nature of true worship, exposing hypocrisy, warning the wicked, and encouraging the pious. (Psa. 50:1-23)
The description of this majestic appearance of God resembles that of His giving the law (compare Exo 19:16; Exo 20:18; Deu 32:1).
above--literally, "above" (Gen 1:7).
heavens . . . earth--For all creatures are witnesses (Deu 4:26; Deu 30:19; Isa 1:2).
my saints-- (Psa 4:3).
made--literally, "cut"
a covenant, &c.--alluding to the dividing of a victim of sacrifice, by which covenants were ratified, the parties passing between the divided portions (compare Gen 15:10, Gen 15:18).
The inhabitants of heaven, who well know God's character, attest His righteousness as a judge.
I will testify--that is, for failure to worship aught.
thy God--and so, by covenant as well as creation, entitled to a pure worship.
However scrupulous in external worship, it was offered as if they conferred an obligation in giving God His own, and with a degrading view of Him as needing it [Psa 50:9-13]. Reproving them for such foolish and blasphemous notions, He teaches them to offer, or literally, "sacrifice," thanksgiving, and pay, or perform, their vows--that is, to bring, with the external symbolical service, the homage of the heart, and faith, penitence, and love. To this is added an invitation to seek, and a promise to afford, all needed help in trouble.
the wicked--that is, the formalists, as now exposed, and who lead vicious lives (compare Rom 2:21, Rom 2:23). They are unworthy to use even the words of God's law. Their hypocrisy and vice are exposed by illustrations from sins against the seventh, eighth, and ninth commandments.
God, no longer (even in appearance) disregarding such, exposes their sins and threatens a terrible punishment.
forget God--This denotes unmindfulness of His true character.
offereth praise-- (Psa 50:14), so that the external worship is a true index of the heart.
ordereth . . . aright--acts in a straight, right manner, opposed to turning aside (Psa 25:5). In such, pure worship and a pure life evince their true piety, and they will enjoy God's presence and favor.