But, for a variety of reasons, some Christians just aren’t used to reading the Old Testament that way. So, if you’re more used to reading the Old Testament simply in terms of ‘God’ rather than the Trinity, here’s some help for you from Martin Chemnitz (a great theologian from the second generation of the Reformation – although, Martin would want you to know that this isn’t something new he came up with, but rather he’s boiling down the principles passed on by a millennium and a half of theologians and Bible teachers before him into 4 rules).
1. ‘When Scripture speaks of God in the plural, it is certain that there is a reference to the plurality of persons.’
Chemntiz insists we should understand these plurals as indications of the Trinity. And he wasn’t blindly holding onto some sort of naïve, pre-critical idea when he argued this. Chemnitz was quite aware of contrary arguments (like the idea of a plural of majesty) but shows that these are ideas that have been ‘recently dreamed up’ in order to find a non-Trinitarian alternative reading.
Instead of turning to such novelties, we should hold onto the ancient understanding of the Christian church, that the plural references to God are ‘hinting at the Trinity in unity and the unity in Trinity.’
2. ‘Wherever you read in Scripture that God is speaking about God, as a person about a person, there you are safe in affirming that the three persons of the Deity are indicated. For when two persons are named at the same time, the person of the Holy Spirit who is speaking in the Scripture is indicated.’
3. ‘When the name of God (Jehovah, Kyrios, LORD) is repeated two or three times in the same sentence, it is certain that a difference in persons is indicated even though obscurely, as in Ps. 67:6-7; Deut. 6:4; Is. 6:3; Num. 6:23-27; Is. 33:22.’
The LORD bless you and keep you;Compare this threefold benediction from the LORD with the Trinitarian benedictions of the New Testament.
The LORD make His face shine upon you,
And be gracious to you;
The LORD lift up His countenance upon you,
And give you peace.
4. ‘Often not only the repetition of names hints at the persons of the Trinity in the Old Testament, but the description is such that of necessity it is manifest that the context pertains to the differences of the persons in the unity of the essence.’
The Angel of the LORD is also an example of this, for He is sent from the LORD and yet He shares the name of the LORD (e.g. Ex. 23:20-21), speaks as the LORD (e.g. Gen. 22:11-12), and delivers as the LORD (e.g. Josh. 2:1).
So there you go, 4 rules for reading to help you see the Triune God in the Old Testament. (If you want to see a bit more of what Chemnitz has to say about these rules, and some more Scripture passages he gives as examples, you can find that on pp.90-91 of the first volume of his Loci Theologici.)