Most of us typically meditate on the truth that we are children of God (1 John 3:1-2), and how marvelous it is that we are his. But Calvin here wants us to meditate on the truth that our adoption by grace into God’s family should magnify Christ’s sonship even more. For what is ours by grace is his by nature.
The apostle Paul loved to meditate on this. He repeatedly called our Lord Jesus “the firstborn”. Calvin mentions two passages in particular, Romans 8:29 and Colossians 1:15. We’ll focus on Romans 8:29. God, before the foundation of the world, had predetermined to work for the good of those who love him and are called according to his purpose (v.28). The hinge between verse 28 and verse 29 is the word “For”, which normally introduces a reason for the previous clause. God works all things together for the good of his own, then, because of his predetermined plan to conform his own to the image of his Son.
Notice the terms “Son”, “firstborn” and “brothers”. God’s plan is to conform us into the image of his Son, so that he would not be an only Child, if you will. His desire is to surround his Firstborn with many siblings who look just like him in holiness and love. And, by doing so, the Father is praised for his grace, and the Son is magnified as the Firstborn, for he pleases the Father so much that he would adopt countless children to reflect his Son’s perfection. To be in God’s family, reflecting the glories of our Big Brother, the Lord Jesus—for believers, all things work together for this good.