The idea of "Unconditional Election" was invented by the Calvinists. Well known Calvinist teacher R.C. Sproul teaches that being chosen by God before the foundation of the world is not based on something foreseen in us:
"The grounds of our election are not something foreseen by God in us but rather the good pleasure of his sovereign will...Reformed theology insists that God's election is based on nothing foreseen in the individual's lives, this does not mean that he makes the choice for no reason at all. It simply means that the reason is not something found in us" [emphasis added] (R.C. Sproul, What is Reformed Theology? [Grand Rapids: Baker Books, 2005], 146,147).
Sproul also says, "The Reformed view holds that we are elected 'unto' faith and justification. Faith is a necessary condition for salvation but not for election" [emphasis added] (Ibid., 145).
The problem with this idea is the mistaken idea that a person can be "in Christ" but not yet saved:
"According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love" (Eph.1:4).
Once a person is "in Him" or "in Christ" he is saved:
"Who hath saved us, and called us with an holy calling, not according to our works, but according to his own purpose and grace, which was given us in Christ Jesus before the world began" (2 Tim.1:9).
"Therefore I endure all things for the elect's sakes, that they may also obtain the salvation which is in Christ Jesus with eternal glory" (2 Tim.2:10).
So we can see that being chosen before the foundation of the world is in regard to salvation since the elect are chosen "in Him." In other words, no one can be chosen "in Him" unless salvation is secured.
The following two verses are both in regard to election and both also tie that election to 'sanctification of the Spirit":
"Elect according to the foreknowledge of God the Father, through sanctification of the Spirit, unto obedience and sprinkling of the blood of Jesus Christ"(1 Pet.1:2).
"But we are bound to give thanks always to God for you, brethren beloved of the Lord, because God hath from the beginning chosen you to salvation through sanctification of the Spirit and belief of the truth" (2 Thess.2:13).
Notice that in the second quoted verse of these two the phrase "through sanctification of the Spirit" is tied to "salvation" so common sense dictates that the phrase has the same meaning in both verses which are speaking of being chosen or elected. In both of these verses the Greek word translated "through" means "of the instrument or means by or with which anything is accomplished...by means of, by (through)" (Thayer's Greek English Lexicon).
So we can see that being chosen to salvation is through the instrumentality of the sanctification of the Spirit. One of the meanings of the Greek word translated "sanctification" is "separation to God...1 Pet.1:2" (Vine's Expository Dictionary of New Testament Words).
Therefore, we can understand that being chosen or elected is through the instrumentality of the Spirit when He separates a person to God. That happens when a person is baptized into the Body of Christ by one Spirit:
"For by one Spirit are we all baptized into one body, whether we be Jews or Gentiles, whether we be bond or free; and have been all made to drink into one Spirit" (1 Cor.12:13).
It is through this baptism that a believer is also baptized or immersed into the death of the Lord Jesus:
"Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death? Therefore we are buried with him by baptism into death" (Ro.6:3-4).
This speaks of the Lord Jesus' vicarious death on Calvary's Cross by which the believer is saved.
When the gospel was first preached to the Gentiles by Paul and Barnabas we read the following about what happened:
"And when the Gentiles heard this, they were glad, and glorified the word of the Lord: and as many as were ordained to eternal life believed" (Acts 13:48).
The Gentiles who believed were ordained to salvation "from the beginning" mentioned here:
"But we are bound to give thanks alway to God for you, brethren beloved of the Lord, because God hath from the beginning chosen you to salvation through sanctification of the Spirit and belief of the truth" (2 Thess.2:13).