Fausset's Bible Dictionary
("my delight is in her".) Jehovah's name for Jerusalem when restored to His favor (Isaiah 62:4); instead of being as now "desolate" and "forsaken." As the prophets naturally mould their prophecies in a form suggested by the facts of the day, Hezekiah's marriage to Hephzibah, Manasseh's mother (2 Kings 21:1), would obviously suggest itself. Hence Isaiah terms restored Jerusalem both Hephzibah and Beulah, i.e. "married." The marriage of Hezekiah moreover was at a late period of his reign, after his sickness and recovery described in Isaiah 38.
Indeed Hezekiah's desire of life in that sickness was mainly because, being childless then, he was leaving no successor to the kingdom (Josephus); to which God's words may refer, "set thine house in order," i.e. make arrangements as to the succession to the throne, That sickness was probably in the 14th year of his reign (Isaiah 36:1). Manasseh was only 12 years old at his father's death; so that if Isaiah's prophecies are at all in the order of their delivery, this late prophecy, chap. 62, concerning Hephzibah would be just at the time of Hezekiah's marriage to her; his reign in all being 29 years, the marriage was after the 14th year and before the 12th year preceding Hezekiah's death, i.e. between the 11th and 17th years of his reign. These undesigned coincidences accord with truth.
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Fausset, Andrew R. Entry for 'Hephzibah'. Fausset's Bible Dictionary. https://www.studylight.org/​dictionaries/​eng/​fbd/​h/hephzibah.html. 1949.