Thou shalt also be a crown of glory - On the application of the word ‘crown’ to a place, see the notes at Isaiah 28:1, where it is applied to Samaria. Some difficulty has been felt by expositors in explaining this, from the fact that a crown or diadem was worn on the head and not held in the hand, and some have supposed that the word ‘crown’ here is equivalent to any ornament which might be either horne in the hand or worn on the head; others have supposed that the reference is to the custom of carrying a chaplet or garland in the hand on festival occasions. But probably the sense is this, ‘Thou shalt I be so beautiful and prosperous as to be appropriately regarded as a splendid crown or diadem. God shall keep thee as a beautiful diadem - the crown of beauty among the cities of the earth, and as that which is most comely and valuable in his sight.’ This is the sense expressed by Gataker and Rosenmuller.
And a royal diadem - Hebrew, ‘A diadem of a kingdom.’ The diadem is the wreath or chaplet, usually set with diamonds, which is “encircled” (צניף tsânı̂yph from צנף tsânaph) to roll or wind around, to encircle) around the head. It here means such as was usually worn by monarchs; and the sense is, that Jerusalem would become exceedingly beautiful in the sight of God.