The writers of the Heidelberg Catechism, one of the most influential confessional documents ever created, thought the doctrine of adoption was important enough to be included in this beautifully written question and answer document. I'm grateful they did. In it they briefly address the relationship between Christ's Sonship and ours.
Question 33. Why is Christ called the "only begotten Son" of God, since we are also the children of God?
Answer: Because Christ alone is the eternal and natural Son of God; but we are children adopted of God, by grace, for his sake.
It's interesting that even before the era of positive adoption language, theological adoption is framed in the Catechism in terms of "natural" sonship vs. sonship by adoption -- rather than "real" sonship vs. sonship by adoption. I conclude from this that you might be able to make an argument from theology for positive adoption terms. If we're thinking about those theological parallels, then saying "they have 3 real kids and 2 adopted" is not just insensitive (a good social reason to avoid language like that), but it's also theologically pernicious! If adoption doesn't create a real parent-child relationship, then what's our relationship to God?
This also has implications for the fringe anti-adoption movement that claims adoption creates a "legal lie" when it establishes a new parent-child relationship. This argument rests on the assumption that BIOLOGY = REALITY or HUMAN DESCENT = TRUE IDENTITY. But St. Paul tells us that under the New Covenant, human descent isn't the primary issue anymore.
Hm ... lots of theological implications that you can post about in the future, Dan. Thanks for your thoughts on adoption.
[...] was so committed to Israel, His adopted son, that He sent His natural Son (see the wording of the Heidelberg Confession on adoption) to deliver him (i.e. Israel) from his habitual sin and prodigal unfaithfulness. Jesus, God’s [...]
[...] was so committed to Israel, His adopted son, that He sent His natural Son (see the wording of the Heidelberg Confession on adoption) to deliver him (i.e. Israel) from his habitual sin and prodigal unfaithfulness. Jesus, God’s [...]