The complete happiness of the redeemed is a kingdom
A kingdom is the top of worldly felicity; there is nothing on earth greater than a kingdom: therefore the hidden weight of the glory in heaven is held forth to us under that notion. But it is not an ordinary kingdom, it is “the kingdom;” the kingdom of heaven, surpassing all the kingdoms of the earth in glory, honour, profit, and pleasure, infinitely more than they do in these excel the low and inglorious condition of a beggar in rags, and on a dunghill.
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The happiness of the redeemed in God’s kingdom includes their reign
“Thy kingdom come. Thy will be done in earth, as it is in heaven” (Matt. 6:10)
The dominion of the saints will be a dominion far exceeding that of the greatest monarch who ever was on earth. They will be absolute masters over sin, which had the dominion over them. They will have a complete rule over their own spirits; an entire management of all their affections and inclinations, which now create them so much molestation: the turbulent root of corrupt affections shall be for ever expelled out of that kingdom, and never be able any more to give them the least disturbance.
Adapted from The Whole Works of Thomas Boston, 8:317-8.