(1.) He adopts us to a state of excellence. It were much for God to take a clod of dust, and make it a star; it is more for him to take a piece of clay and sin, and adopt it for his heir.
(2.) God adopts us to a state of liberty. Adoption is a state of freedom; a slave being adopted is made a free man. ‘Thou art no more a servant but a son.’ Gal 4:7. How is an adopted son free? Not to do what he lists; but he is free from the dominion of sin, the tyranny of Satan, and the curse of the law. He is free in the manner of worship. He has God’s free Spirit, which makes him free and cheerful in the service of God; he is ‘joyful in the house of prayer.’ Isa 56:7.
(3.) God adopts us to a state of dignity. He makes us heirs of promise, he installs us into honour. ‘Since thou wast precious in my sight, thou hast been honourable.’ Isa 43:4. The adopted are God’s treasure; Ex 19:5; his jewels; Mal 3:17; his first-born; Heb 12:23. They have angels for their life-guards. Heb 1:14. They are of the blood royal of heaven. 1 Jn 3:9.
The Scripture has set forth their spiritual heraldry; they have their escutcheon or coat-armour; sometimes the lion for courage; Pr 28:1; sometimes the dove for meekness; So 2:14; sometimes the eagle for flight; Isa 40:31:Thus you see their coat of arms displayed.
(4.) What is honour without inheritance? God adopts all his sons to an inheritance. ‘It is your father’s good pleasure to give you the kingdom.’ Lk 12:32. It is no disparagement to be the sons of God. To reproach the saints, is as if Shimei had reproached David when he was going to be made king. Adoption ends in coronation. The kingdom God gives his adopted sons and heirs excels all earthly monarchies.
(1:) In riches. ‘The gates are of pearl, and the streets of pure gold, as it were transparent glass.’ Rev 21:21.
(2:) In tranquillity. It is peaceable, and the white lily of peace is the best flower in a prince’s crown. Pax una triumphis innumeris melior [one peace is better than innumerable triumphs]. No divisions at home, or invasions abroad; no more the noise of the drum or cannon; but the voice of harpers harping is the hieroglyphic of peace. Rev 14:2.
(3:) In stability. Other kingdoms are corruptible; though they have heads of gold they have feet of clay; but the kingdom into which the saints are adopted runs parallel with eternity, it is a kingdom that cannot be shaken. Heb 12:28. The heirs of heaven reign for ever and ever. Rev 22:5.’
(Thomas Watson, A Body of Divinity)