Ezekiel 28:12 KJV Son of man, take up a lamentation upon the king of Tyrus, and say unto him, Thus saith the Lord GOD; Thou sealest up the sum, full of wisdom, and perfect in beauty.

let's define "sum" in the lexicon strong's concordance; H8508 - sum, pattern

Outline of Biblical Usage [?]
measurement, pattern, proportion

scripture cross-references to "Eze 28:12", where it says, "Thou sealest up the sum" are below:

Ezekiel 28:2 KJV
Son of man, say unto the prince of Tyrus, Thus saith the Lord GOD; Because thine heart [is] lifted up, and thou hast said, I [am] a God, I sit [in] the seat of God, in the midst of the seas; yet thou [art] a man, and not God, though thou set thine heart as the heart of God:

scripture cross-reference to "Eze 28:2", where it says, "I sit in the seat of God" is below:

Ezekiel 28:14 KJV
Thou [art] the anointed cherub that covereth; and I have set thee [so]: thou wast upon the holy mountain of God; thou hast walked up and down in the midst of the stones of fire.

scripture cross-references to "Eze 28:14", where it says, "upon the holy mountain of God;" are below:

Isaiah 14:12 KJV
How art thou fallen from heaven, O Lucifer, son of the morning! [how] art thou cut down to the ground, which didst weaken the nations!

Isaiah 14:13 KJV
For thou hast said in thine heart, I will ascend into heaven, I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation, in the sides of the north:

Isaiah 14:14 KJV
I will ascend above the heights of the clouds; I will be like the most High.

Isaiah 14:15 KJV
Yet thou shalt be brought down to hell, to the sides of the pit.

References:

https://www.blueletterbible.org
Lexicon/Strong’s Concordance
https://www.quora.com


https://www.quora.com/What-do-you-think-of-Ezekiel-28-12-17-What-is-meant-by-this