2Th 2:13 But we are bound to give thanks to God always for you, brethren beloved by the Lord, because God from the beginning chose you for salvation through sanctification by the Spirit and belief in the truth
First of all, the expression "from the beginning" does not mean before the beginning of time. It refers to a starting point in time.
1Jo 2:7 Brethren, I write no new commandment to you, but an old commandment which you have had from the beginning. The old commandment is the word which you heard from the beginning.
From the beginning here refers to the beginning of the ministry of the Lord Jesus Christ when He taught the disciples the commandment to love. They did not hear the commandment before the beginning, in eternity past, before the creation of the world. No! From the beginning refers to a point in time here on earth.
Mt 19:8 He said to them, "Moses, because of the hardness of your hearts, permitted you to divorce your wives, but from the beginning it was not so.
From the beginning here refers to the beginning of the marriage institution when God created Adam and Eve. It does not refer to eternity past, before the creation of the world. From the beginning, man and woman was created as one. There was no divorce.
Lu 1:2 just as those who from the beginning were eyewitnesses and ministers of the word delivered them to us,
From the beginning here refers to the beginning of the ministry of the Lord Jesus Christ. It does not refer to eternity past.
In 2nd Thes. 2:13, the expression "from the beginning" does not point back to eternity past. It refers to a point of time at the beginning of the preaching of the Gospel by Paul there in Thessalonica. This is not about God choosing who will be saved in eternity past.
Second, the word salvation here based on the context means salvation from the coming Tribulation Period. Paul has been talking about the Tribulation Period, the coming of the Anti-Christ, his deluding influence and the wrath that will befall the entire planet (read 2 Thes. 2:1-12)
The Thessalonians were apprehensive that maybe they have entered that frightful cataclysmic stage in world history. Paul wrote to comfort them. God, when they believed the Gospel message, did not appoint them to experience the wrath that the world will experience at the Tribulation Period.
He has been talking about this in his first letter to them:
1Th 1:10 and to wait for His Son from heaven, whom He raised from the dead, even Jesus who delivers us from the wrath to come.
1Th 5:2 For you yourselves know perfectly that the day of the Lord so comes as a thief in the night.
The day of the Lord here refers to the Great Tribulation Period.
1Th 5:9 For God did not appoint us to wrath, but to obtain salvation through our Lord Jesus Christ,
God did not appoint the the Church to experience the coming wrath of the Tribulation Period. No, they were appointed to be saved from it.
