Metzudat David on Zechariah
shall join – Then many idolaters will join to the Lord and will be His nation, believing in Him. Nevertheless, I will dwell among you and not among the many idolaters: and you shall know – Then, when He causes His Presence to dwell among you alone, you will know that the Lord sent me to you. That is to say, the primary purpose and cause is spoken in regard to you: