Seeing it is a righteous thing with God to recompense tribulation to them that trouble you; [KJV]
ειπερ δικαιον παρα θεω ανταποδουναι τοις θλιβουσιν υμας θλιψιν [TR, undisputed]
Paul begins his epistle referring to ‘God Father our’ and ‘Lord Jesus Christ’ - all five nouns being accusative due to the use of the preposition en - and referring, again, to ‘God Father our’ and ‘Lord Jesus Christ’ - all five nouns this time being genitive due to the influence of the preposition apo.
That both of the concepts (that is also to say ‘the persons’) being referred to in the first occasion of mention are presented in the anarthrous form, that is to say without an article, is quite understandable. For this is the introduction of concept. Later, we would expect the anaphoric article to be added in order to refer back to, or to locate to, these persons.
That the two concepts, on the second occasion of mention, are both, again, anarthrous is also understandable since Paul is referring to the knowledge of divine person within two different congregations - one in the assembly at Thessalonica and one located within the fellowship of the three ministers, Paul Silvanus and Timothy : wherever (Athens ?) they may have been at that time.
In the same sense, elsewhere, Paul speaks of ‘their Lord and ours’, 1 Corinthians 1:2. Thus it is not unexpected to see him use this expression twice without article, not referring back in the second to the first. He gives regard to the dwelling in each assembly of an individuality of presence and thus does not assume to use the anaphoric article in the second case to refer to the first case. In each gathering, there is a Presence. That Presence is individual to each assembly.
Thus far, as I say, all is understandable.
Paul proceeds :
and immediately, he uses the anaphoric article in verse 3, referring, in thanks, back to θεος in verse 1. And we would no doubt understand this to be a reference to God Father, the first person of the two mentioned.
Paul again uses the anaphoric article in verse 4, mentioning assemblies of θεος, and referring back, again, to what one would understand to be God Father.
In verse 5 Paul speaks of the righteous judgment of God (expressed in the assembly) and, yet again, uses the anaphoric article to refer back to God Father in verse 1.
Thence also, once more in verse five, regarding the kingdom of God, the anaphoric article is used in reference back to verse 1, to ‘God Father’.
Then in verse six, Paul uses θεος without an article. The noun is, on this occasion, anarthrous. Thus, Paul is signifying a new concept. He has not - yet - mentioned the concept which he now introduces. (Else, would he use an anaphoric article to refer back to it.)
Previously, Paul used the term θεος specifically, coupling it to 'Father', and identifying one individual.
Now he uses the term θεος generically - without the defining and identifying quality of the article and without the anaphoric article referring to the previously specific mention of the concept - and he now extends the concept to more than one person.
On this occasion Paul introduces the idea of recompense to those who have caused tribulation to others. This recompense occurs upon the revelation of Jesus Christ who, with the angels of his power, in a fire of flame, awards vengeance to them that know not θεος (again, no article).
Paul does not, on these two occasions in verse 6, refer ‘Theos’ back to ‘God Father’ in verse 1.
Is Paul widening the concept of ‘Deity’ - which he first applied to ‘Father’ - and does he now extend the concept (indicating its extension in application) to include both Father and Son ?
Having spoken, firstly, of the presence of God Father in the assembly at Thessalonica and having extended a blessing of grace and peace from within the ministerial fellowship (and having spoken of Jesus Christ as a separate entity, previously) does Paul now extend the concept of Deity to include - also - the descending Lord Jesus Christ who brings Divine recompense upon those who have persecuted the faithful who believe in God through the Son of God, Jesus Christ ?
Mentioned in resurrected and ascended glory, Lord Jesus Christ is - now, in Paul‘s narrative - revealed from heaven, and revealed now (for the first time) with angelic power in attendance, seen in Divine authority recompensing his enemies to whom, heretofore, he had been required to give sufferance :
Sit thou, on my right hand, until I make thine enemies thy footstool, Matthew 22:44 ; Rule thou in the midst of thine enemies. Psalm 110:2. [KJV]
Is there another justifiable grammatical reason for Paul’s use of the anarthrous θεος in this verse ?
What other grammatical reason can there be for not using the anaphoric article in verse six ?
Thereafter, in verses 11 and 12, Paul uses the anaphoric article, referring back to verse 1, speaking of ‘the calling of the God of us’ and ‘the grace of the God of us and of Lord Jesus Christ’ in the same vein as that in which he began the chapter.
Does the use of the anarthrous θεος in verse six, together with - elsewhere in the chapter - the anaphoric article, give us an insight into Paul’s understanding of the true nature of Deity as revealed in Jesus Christ - in whom is revealed ‘God Father‘ ?
Or is there another grammatical explanation ?