5. The Greek is, "Not that we are (even yet after so long experience as ministers) sufficient to think anything OF ourselves as (coming) FROM ourselves; but our sufficiency is (derived) FROM God." "From" more definitely refers to the source out of which a thing comes; "of" is more general.
to think—Greek, to "reason out" or "devise"; to attain to sound preaching by our reasonings [Theodoret]. The "we" refers here to ministers (2Pe 1:21).
anything—even the least. We cannot expect too little from man, or too much from God.