Albert Barnes Commentary Zechariah 12:8

"In that day shall Jehovah defend the inhabitants of Jerusalem: and he that is feeble among them at that day shall be as David; and the house of David shall be as God, as the angel of Jehovah before them." — Zechariah 12:8 (ASV)

In that day the Lord shall defend the inhabitants of Jerusalem; and he who is feeble, rather, he who stumbleth among them, shall be as David - The result of the care and the defense of God is here wholly spiritual, “the strengthening of those who stand, and the raising up of those who fall.” It is not simply one who is feeble, but one “stumbling” and ready to fall, who becomes as David, the great example of one who fell, yet was raised. Daniel says of a similar trial-time, And some of those of understanding shall stumble, to try them and to purge and to make them white, to the time of the end (Daniel 11:35).

Ribera: “Such care will God have in protecting the sons of the Church, when it will be infested with persecutions, that he who has fallen through human infirmity, either deceived by heretics or overcome by fear of tortures, will arise more fervent and cautious, and with many tears will make amends for his sins to God, as David did. ‘He who stumbled shall be as David,’ because the sinner returns to repentance. This is not said of all times, nor of all (for many have stumbled, who never rose) but chiefly of the first times of the Church and of people of great sanctity, such as many were then.”

And the house of David shall be as God - Those who stumbled became really like David; but he, though mighty and a great saint of God, though he once fell, was man. How then could the house of David be really like God? Only fully in Him, who, being in the form of God, thought it not robbery to be equal with God (Philippians 2:6); who said, He who hath seen Me, hath seen My Father also (John 14:9); I and the Father are one (John 10:30).

And this the prophet brings out by adding, as the Angel of the Lord before them, that is, that one Angel of the Lord, in whom His very Presence and His Name was; who went before them, to guide them (see “Daniel the prophet” pages 519-523). Otherwise, having said, “like God,” it would have lessened what he had just said, to add, “like the Angel of the Lord.”

Our Lord prayed for those who are truly His, As You, Father, are in Me and I in You, that they may be one in Us; that they may be one as We are one, I in them, and You in Me, that they may be perfect in one (John 17:21–23); and Paul says, Christ is formed in us (Galatians 4:19); Christ dwelleth in our hearts by faith (Ephesians 3:17); Christ liveth in me (Galatians 2:20); Christ is in you (Romans 8:10); Christ is our life (Colossians 3:4); Christ is all and in all (Colossians 3:11); we grow into Him which is the Head, even Christ (Ephesians 4:15); we are in Christ (Romans 16:7; 2 Corinthians 5:17; Galatians 1:22); and Peter, we are partakers of the divine nature (2 Peter 1:4); and John, As He is, so are we in this world (1 John 4:17).

Then in a degree the glory of Christ passes over to those who dwell in Him, and in whom He dwells by the Spirit, as Paul says; You received me, as an angel of God, as Christ Jesus (Galatians 4:14).