Synopsis of the Books of the Bible, by John Nelson Darby, [1857-62], at sacred-texts.com
In Psalm 78 the conduct of Israel is discussed by wisdom, historically as regards the whole people, but with very important principles brought out. There was not only a redemption of old, to which faith recurred, but a testimony given, and a law to guide Israel's ways, that they should make them known to their children. But the fathers had been a stubborn and rebellious generation. Now, the law and the testimony were given that the children might not be like their fathers; but they were, and their history is here brought out. God, therefore, chastened them; there was direct open government in respect of their ways. For all this they sinned still. At the moment of chastisement they turned to Him. Nevertheless they did but flatter Him with their mouth, their heart was not right with Him, nor they stedfast in His covenant. But He showed compassion, also forgave, remembered they were but flesh. Yet after Egyptian signs they forgot Him; brought into the land, they turned to idolatry. When God heard this, He was wroth and greatly abhorred Israel. On the ground of this government, under law and testimony and compassionate mercy, Israel was wholly given up, the tabernacle forsaken, the ark delivered into captivity and the enemies' hand. The people also were delivered over to judgment. But Jehovah's love to His people in grace was not weakened, and the sorrow they were brought into called out that love. He awoke, as one out of sleep, and smote His enemies, and put them to a perpetual shame. But now He had interfered in grace in His own proper love to His people. It was not governmental blessing on condition of obedience, but the interference of grace, when disobedience had, on the principle of government, brought in complete judgment, in spite of compassion and mercy. Sovereign mercy now had its place. Old blessings had put Joseph as natural heir; he had the rich and double portion. God chose Judah. He chose Zion. This gave it its importance. It is the place of love in grace, when all had failed under law, even with the fullest compassionate patience. He built His sanctuary. That is not directly presented as the subject of electing goodness, but He chose David when in the humblest condition, who then fed His people.
In this most beautiful psalm we have the most important principles possible. Viewing Israel as established on the ground of government in Sinai, on law mixed with compassion, Israel had entirely failed, was abhorred, cast off. A total breach had been made; the ark of the covenant, the link between Israel and God, the place of propitiation, and His throne, given up to the enemy. But God, whose sovereign love to His people had come in in power to deliver, had chosen Judah, Zion, David, and set up a link in grace, and by deliverance after failure. Faith can go back to God's works in redemption, but not to man's conduct under law. Psalm 78 is the converse of Psalm 77. Yet in Israel all this is declared to produce that which grace will effect in the last day that value for the law in the heart which will make them teach it to their children (compare Gen 18:17-19; see Exodus 34). Mercy put Israel again under the condition of obedience. Here power delivers, after they have failed even under this, and judgment is come, God acting according to His mind of love. Pure law they never were under in fact; the tables never came into the camp (compare 2 Corinthians 3). Moses' face shone only when he had seen God, when he went up the second time accepted in grace; but for Israel, this was putting them back under law. It is grace, and law brought in after it, which is death and condemnation. This is impossible with substitution; but this place, of course, Moses could not take. "Peradventure I shall make an atonement for your souls." "Blot me out, I pray you." No, was the answer; the soul that sins, it will I blot out. This was law and (as we see here, and as is definitely stated in 2 Corinthians 3) ruin.