Briefly ‘because’ & ‘for’ as conjunctions share the same meaning as ‘since, for the reason that’. We’ll use an example to explain the difference: We play soccer because (~ for reason that; since; for) we enjoy the game. You can say Because we enjoy soccer, we play the game. You can’t however say *For we enjoy soccer, we play the game. ‘Because’ can be used to introduce a subordinate clause (we enjoy soccer) that gives the reason for the main clause (we play the game). ‘For’ can only introduce a clause following the main clause. Its use is more formal in that sense. We therefore can say We play soccer, for we enjoy it.