And for this cause we also (kai dia touto kai hēmeis). Note kai twice. We as well as you are grateful for the way the gospel was received in Thessalonica.
Without ceasing (adialeiptōs). Late adverb for which see note on 1Th 1:3 and for eucharistoumen see note on 1Th 1:2.
The word of the message (logon akoēs). Literally, the word of hearing, as in Sir. 42:1 and Heb 4:2 ho logos tēs akoēs, the word marked by hearing (genitive case), the word which you heard. Here with tou theou (of God) added as a second descriptive genitive which Paul expands and justifies.
Ye received it so (paralabontes) and accepted or welcomed it (edexasthe) so, not as the word of men (ou logou anthrōpōn), but as the word of God (alla logon theou), as it is in truth (kathōs alēthōs estin). This last clause is literally, as it truly is. Paul had not a doubt that he was proclaiming God’s message. Should any preacher preach his doubts if he has any? God’s message can be found and Paul found it.
Worketh in you (energeitai en humin). Perhaps middle voice of energeō (en, ergon, work) late verb, not in ancient Greek or lxx, but in papyri and late writers (Polybius, etc.) and in N.T. only by Paul and James. If it is passive, as Milligan thinks, it means “is set in operation,” as Polybius has it. The idea then is that the word of God is set in operation in you that believe.