No, the poet doesn't believe in anything. He would like to believe. It's through the poem he hopes to believe in something. Certainties in these poems are to be considered hope or wishes. The poem itself believes. But something which renders the poem credible, doesn't have to be that for the maker. Look: you don't write poems about things that are obvious for you. Then they would just become little tracts. A poem tries, follows a path, is something you don't know for yourself, or something you don't believe in yet. In that sense a poem shapes its creator. After each succesful poem he has become a different person.
Jellema, talking about his book 'Ongeroepen'.