The above states HOW we will be saved.
Not WHO will be saved.
2 Thessalonians 2:13-15 Your verse
13But 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.
14It was for this He called you through our gospel, that you may gain the glory of our Lord Jesus Christ.
15So then, brethren, stand firm and hold to the traditions which you were taught, whether by word of mouth or by letter from us.
The above states that God has chosen us to be saved THROUGH SANCTIFICATION BY THE SPIRIT.
This is a HOW, not a WHO.
Also, Verse 15 exhorts us to HOLD TO THE TRADITION which we are taught....
Why?
To maintain our salvation, a concept not in keeping with Perseverance of the Saints.
Paul taught thay salvation can be forfieted, proving that Perseverance of the Saints is not a correct teaching.
Here is what Paul taught:
Colossians 1:21-23
21And although you were formerly alienated and hostile in mind, engaged in evil deeds,
22yet He has now reconciled you in His fleshly body through death, [this is HOW we are saved] in order to present you before Him holy and blameless and beyond reproach— [this is WHY we are saved].
23if indeed you continue in the faith firmly established and steadfast, and not moved away from the hope of the gospel that you have heard, which was proclaimed in all creation under heaven, and of which I, Paul, was made a minister.
We will be saved IF we persevere to the end, IF we CONTINUE in the faith....
The bible teaches us God's laws,
Calvin teaches man's laws.