Nevertheless, I was pleased to read Fred Sanders short remarks on The Trinity between OT and NT. While reading it, it brought to mind my fond memories of doorbells ah ringing.
In the fullness of time, the one God revealed that he eternally exists as Father, Son, and Holy Spirit, and the doctrine of the Trinity is a biblical doctrine. But if you ask where the Trinity is clearly declared in scripture, you should take care to avoid certain common errors. One error is to dive immediately into prooftexting the doctrine by trying to locate verses which explicitly teach it.
Where in the Bible is the Trinity revealed? Not in the Old Testament, which looks forward to the revealing of the Son; and not in the New Testament, which looks backward to the revealing of the Son. It is revealed in the historical events that take place between the testaments, the events which fulfill the expectation of the Old Testament and provoke the writing of the New Testament. The Trinity is revealed when the Trinity appears in history, when the Father sends the Son and pours out the Spirit on all flesh
This explains why the New Testament almost offhandedly refers to the Trinity, presupposing it and never bothering to present it as a new idea. The fact that the Son has appeared for our salvation is behind every line of the New Testament, is the main point, is what’s New and what’s Testament about the New Testament.
The Trinity is in the Bible, not in the OT or the NT, but between them. “Between” does not mean in the intertestamental period of the Maccabees and such. “Between” does not mean the blank sheet of paper that divides the two testaments in your Bible. “Between” means in the central events on which all salvation history turns, the sending of the Son and the outpouring of the Spirit