Thou wentest forth for the salvation of thy people, even for salvation with thine anointed; thou woundedst the head out of the house of the wicked, by discovering the foundation unto the neck. Selah. Thou wentest forth for the salvation of thy people - Their deliverance would not have been effected but through thy interference.
For salvation with thine anointed - That is, with Joshua, whom God had anointed, or solemnly appointed to fill the place of Moses, and lead the people into the promised land. If we read, with the common text, משיחך meshichecha, "thy anointed," the singular number, Joshua is undoubtedly meant, who was God's instrument to put the people in possession of Canaan: but if, with several MSS. and some copies of the Septuagint, we read משיחיך meshicheycha, "thy anointed ones," the Israelites must be intended. They are frequently called God's anointed, or God's saints. The sense is very far-fetched when applied to Jesus Christ.
Thou woundedst the head out of the house of the wicked - This alludes to the slaying of the first-born through all the land of Egypt. These were the heads of the houses or families.
By discovering the foundation unto the neck - The general meaning of this clause is sufficiently plain: the government of these lands should be utterly subverted; the very foundations of it should be razed. But what means unto the neck, עד צואר ad tsavvar? Several critics read עד צור ad tsar, "Unto the Rock," that on which the house is founded: and this very intelligible reading is obtained by the omission of a single letter, א aleph, from the word צוער, This conjecture has been adopted by Newcome, though unsupported either by MS. or version. But is the conjecture necessary? I think not: read the verse as it ought to be read, and all will be plain. "Thou hast wounded the head even unto the neck, in the house of the wicked, by laying bare the foundation." The whole head, neck, and all are cut off. There was no hope left to the Egyptians, because the first-born of every family was cut off, so that the very foundation was laid bare, no first-born being left to continue the heirship of families.