I, the Teacher, was king over Israel in Jerusalem.
Solomon, having asserted in general that all is vanity, and having given some general proofs of it, now takes the most effectual method to evince the truth of it, 1. By his own experience; he tried them all, and found them vanity. 2.
Commenting on Ecclesiastes 1:12-18
I the preacher was king over Israel in Jerusalem. Solomon having given a general proof of the vanity of all things here below, and of the insufficiency of them to make men happy, proceeds to particular instances, and begins with human wisdom and knowledge, which of all things might be thought to be most conducive to true happiness; and yet it falls short of it...
Resumption of Ecc 1:1, the intermediate verses being the introductory statement of his thesis. Therefore, "the Preacher" (Koheleth) is repeated. was king--instead of "am," because he is about to give the results of his past experience during his long reign. in Jerusalem--specified, as opposed to David, who reigned both in Hebron and Jerusalem; whereas Solomon reigned only in Jerusalem.