Thou sealest up the sum, etc. The noun is found only there and in Ezekiel 43:10, where it is translated "pattern," but is cognate with the word rendered" tale" (equivalent to "measure") of Exodus 5:13, and "measure" in Ezekiel 45:11.
The probable meaning is, Thou settest the seal to thy completeness (perfection). Thou deemest that thou hast attained the consummation of all beauty and wisdom. The LXX. and the Vulgate give, "Thou art a seal;" and this suggests a parallelism with Jeremiah's works to Coniah (Jeremiah 22:24).
The words were, of course, written with a keen irony. This was what the King of Tyro thought of himself.