And he shall pass over to his stronghold for fear, and his princes shall be afraid of the banner,
says the LORD, whose fire is in Zion, and his furnace in Jerusalem.
Read Chapter 31
Bede
AD 735
If the breads of the furnace that were baked in secret signify the interior devotion of the mind of the faithful confirmed by the fire of charity, breads which were also commanded by the law to be offered in the sacrifice of the Lord, it is most fitting that the hearts which were made to burn constantly with the flame of intimate love and virtue and to beget words are symbolized through the furnaces in which the same breads were baked. The prophet spoke beautifully about these things when he referred to “the Lord whose fire is in Zion and whose furnace is in Jerusalem.” It is also written: “Did our hearts not burn within us when he spoke along the way and opened the Scriptures to us?” - "Three Books on Ezra and Nehemiah 3"
Of this love that is begun here to be perfected from the sight of the Lord in the eternal kingdom Isaiah rightly speaks, saying, “The Lord lives, whose fire is in Zion, and his furnace in Jerusalem.” It is, however, greater to be a furnace than a fire because a fire can also be small, but a larger flame is kindled in a furnace. Zion truly is said to be speculation but Jerusalem the vision of peace. Truly we sometimes catch a glimpse of our peace here in order there later to see it fully. Therefore through the Lord’s love the fire is in Zion and his furnace in Jerusalem because here we burn in some measure with the flames of his love when we glimpse him, but there we shall burn totally when we shall fully see him whom we love. - "Homilies on Ezekiel 2.9.10"
The prescription of the law must be taken in the more spiritual sense. For there is a spiritual seed which through charity and the fear of God is conceived in the womb of the soul, which in turn travails and brings forth the spirit of salvation. It is in this sense that the passage is to be taken which reads, “Blessed is he who has seed in Zion and kindred in Jerusalem.” What, indeed! Even though one is a fornicator, a drunkard or an idolater, will he be blessed, provided only that he has seed in Zion and kindred in Jerusalem? No one in his right mind would say that. - "Orthodox Faith 4.24"