Synopsis of the Books of the Bible, by John Nelson Darby, [1857-62], at sacred-texts.com
Psalm 79 refers, in the plainest terms, to the inroad of the heathen, especially the northern army (Joel 2 refers to a second attack, in which the cry of the psalm is answered; Isaiah speaks of both), who had laid waste Jerusalem and the temple, and shed the blood of the servants of Jehovah. There is the owning of former sins, and mercy looked to tender mercies. The plea is the plea called for in Joel 2, and referred to in previous psalms (42 and 43), "why should the heathen say Where is their God?" and it demands that He may be known by the avenging the blood of His servants. Thus His people and the sheep of His pasture would give Him thanks for ever. Jehovah's anger is seen, and so far there is faith to say How long? That is, though covenant mercies are not enjoyed by the remnant (yea, quite the contrary), yet faith looks to them, and sees Jehovah angry with His people; hence if such, and He thus in relationship with them, He cannot give them up. It is only "How long?" Yet the direct cry is to God, even here, not Jehovah. Israel is not restored to his covenant place. There he will be in known covenant relationship, and then in grace, nor will this ever be lost sight of. Here they were not, but cast out on their failure under a conditional covenant, and though faith in promises sustained them, the new covenant was not entered into; they stood outside blessing, looking backward and forward, having nothing now. This is never the Christian's state. In applying it to himself he makes himself a Jew. For while Christ is hidden on high as to them, the Holy Ghost is come down to us while He is there, and we know that He is accepted and glorified as having stood for us, and that we are in Him.