the sonship of believers (Barth)

Obviously the New Testament concept of divine sonship cannot compete in any sense with that of the divine sonship of Jesus Christ. On the contrary, it is absolutely dependent on this. The fathers made the distinction that Jesus Christ is Filius Dei natura while believers are filii Dei adoptione. They can be this adoptione because Jesus Christ is so natura. The constant indicatives underline what the New Testament says of believers, that they are (Rom. 8:14), we are (Rom. 8:16), we are called and are (1 Jn. 3:1), we are now (1 Jn. 3:2), you are (Gal. 4:6), and even you all are (Gal. 3:26) sons or children of God.

In a decisive passage Paul mentions only one thing in which everything is obviously included for him, v. 15, Gal. 4:6. Remarkably, and certainly not by accident, this is the same cry as the Gospel narrative (Mk. 14:36) puts on the lips of Jesus when He is at prayer in Gethsemane. So then, in this form, the Son of God is the prototype of the sonship of believers.

Barth, K., Bromiley, G. W., & Torrance, T. F. (2004). Church dogmatics, Volume V: Index, with Aids for the Preacher (469). London; New York: T&T Clark.