The word also
(Gk. καὶ/kai) in we also thank God
could be taken with we
or with the verb thank.
A proper evaluation of the options requires fairly technical arguments which are beyond our scope here.1,2,3 I simply note that the interpretation which seems to me to be most consistent with the context is that the also
should be taken with the verb thank,
and that Paul is here expressing an additional reason for thanking God (i.e. additional to the reasons given in chapter 1).4
13 And we also thank God constantly for this, that when you received the word of God, which you heard from us, you accepted it not as the word of men but as what it really is, the word of God, which is at work in you believers.