First, let me start by thanking you for actually attempting to discuss bible study and theology.
Here is the NASB version of our verse:
13 But we should always give thanks to God for you, brethren beloved by the Lord, because God has chosen you from the beginning for salvation through sanctification by the Spirit and faith in the truth.
Lets see if you see what I see: God has chosen you [the Thessalonians] from the beginning for salvation. So our first question in considering when God made the choice, is what does "from the beginning" refer to? Calvinism asserts this refers to the creation week, but even if that mistaken view is accepted, from identifies the action as since or after creation, not before. Whereas Ephesians 1:4 refers to before the foundation of the world, meaning before creation. So I see that the Calvinistic view does not fit the time line.
Why would you identify "from the beginning" as from "creation week?" The word "apo" is translated here "from" but it is also acceptable to translate it "in" or "since." The word is indicating a point in time. Because Scriptures build upon each other, you cannot have Paul stating in one place "before the foundations" and not consider that "from (in, since) the beginning" is not a restatement.
Next, God has chosen you how? Through sanctification and faith in the truth. Calvinism again, or at least some Calvinists, try to say that the through sanctification and through faith applies to "for salvation" rather than applying to "chose you." But that dog will not hunt. See 1 Peter 1:1 where again scripture says we were chosen by being set apart.
I suppose you mean 1 Peter 1:2.
Elect according to the foreknowledge of God the Father, through sanctification of the Spirit, unto obedience and sprinkling of the blood of Jesus Christ: Grace unto you, and peace, be multiplied.
The first verse calls the elect, "strangers" which would also be better as a resident foreigner or pilgrim.
I see the "elect" were chosen according to the foreknowledge of God. (this is predestination)
I see sanctification (being set apart) of (or by) the Spirit (Holy Spirit).
I see the purpose was for Obedience
I see the final result in the Sprinkling of blood (purification)
What I don't see is any conflict of what God would expect of any believer after they are saved.
The actual salvation was by God's choosing of the elect. Which agrees with 2 Thess.
Next, lets discuss your view of "through faith in the truth."
Here is what you said: I see God doing this through sanctification (being set apart) by the Spirit (Holy Spirit) and the belief (credence, reliability, veracity) of the truth.
You say God doing "this." A tad unclear as to whether "this" refers to salvation, the Calvinistic view, or election for salvation. I assume you are saying God saving us through sanctification and belief of the truth. Which of course is not what the verse actually says.
"this" is referring to the processed result of salvation. One cannot be saved and not be sanctified. The sanctification is split into two items by Paul - the Holy Spirit's work and the "conditioning" (so to speak) that every believer experiences as they exercise the veracity (belief) of the truth.
Question: How can we have knowledge -faith - in the truth before the foundation of the world and before we have been created? Answer, we cannot. Therefore 2 Thessalonians 2:13 puts our individual election for salvation as occurring during our lifetime after we have believed in the name of Jesus.
It is not the least inconsistent with Scriptures for God to have foreknowledge and make choices in Christ before the foundations of the world were even set (or reestablished - depending on your view of Gen.).
It is not OUR knowledge, or faith, or even existence that hinges God's foreknowledge.
In more than one place God specified knowledge of the unborn and even foretold events and requirements (specific details) about the yet to be conceived.
Consider a few examples of God foreknowledge at work directly telling parents of the yet to be born: Abraham, Issac, Sampson's parents, Zacharias, Mary
One needs only to look at the prophecies of Christ to see how your statement is week.