The error of replacement theology arises chiefly from not understanding the relativity theory of time & Judgment which only the wise men of God know as Scripture states in the verse below:

“Whoso keepeth the commandment shall feel no evil thing: and a wise man’s heart discerneth both time and judgment.” (Ecclesiastes 8:5)

What does it mean “literally” that “all Israel is not all Israel”?

The “not all Israel are Israel” is mentioned by Apostle Paul to be true “relative” to the current “time” (New Testament Age). It’s not an “absolute” statement. Eventually that verse where it means “all Israel” will come True (absolutely) because in the same breath Paul says not to be “ignorant of the mystery or secret” that “All Israel will be Saved” (which we know will come to pass somewhere in the “coming age” after the end of our current New Testament age).

Israel’s army is not God’s army (no Scripture in the New Testament states it and furthermore, there is no army amongst the earliest Christians who believed in Christ centered Universalism up to 500 AD. The false teaching of Christian army came out of Rome via Augustine of Hippo’s Scriptureless (NT) justification of it in his infamous “Just War” treatise”.

P/S:

This is why Scripture refers to the “first advent of the spiritual children of Israel being those who believe” relative to being an Israelite “believer”.

That particular chapter is describing the salvation of physical Israel (who descended from Abraham literally). The other passages of Scripture highlight that the “gentile believers” too are “children of promise” through Abraham though we are not physically descended from him!

But being an Israelite or a gentile “believer” is no distinction since later the case is built up to mean we’re all one in Christ… For there is no Jew, Greek… Etc.

Why the Bible writes of the distinction between Israel (physical & spiritual) etc? Simple: to explain the “engineering” of how God removes all these “distinctions” to bring about eventually His One Plan to “gather in One all things in Christ” (step by step) and to “reconcile all things to Himself” (in the end).