TRUTH 2 Thessalonians 2:13-14

But we ought always to thank God for you,brothers and sisters loved by the Lord, because God chose you as firstfruits to be saved through the sanctifying work of the Spirit and through belief in the truth. He called you to this through our gospel, that you might share in the glory of our Lord Jesus Christ.

But we ought always to thank God for you 
Romans 1:8  First, I thank my God through Jesus Christ for all of you, because your faith is being reported all over the world.

because God chose you as firstfruits 
Ephesians 1:4-6  For he chose us in him before the creation of the world to be holy and blameless in his sight. In love he predestined us for adoption to sonship through Jesus Christ, in accordance with his pleasure and will--to the praise of his glorious grace, which he has freely given us in the One he loves.

to be saved 
1 Thessalonians 5:9  For God did not appoint us to suffer wrath but to receive salvation through our Lord Jesus Christ.

through the sanctifying work of the Spirit 
1 Peter 1:1-2  Peter, an apostle of Jesus Christ, To God's elect, exiles scattered throughout the provinces of Pontus, Galatia, Cappadocia, Asia and Bithynia, who have been chosen according to the foreknowledge of God the Father, through the sanctifying work of the Spirit, to be obedient to Jesus Christ and sprinkled with his blood: Grace and peace be yours in abundance.

He called you to this 
Romans 8:28  And we know that in all things God works for the good of those who love him, who have been called according to his purpose.
Romans 11: 28-29  As far as the gospel is concerned, they (Israel) are enemies for your sake; but as far as election is concerned, they are loved on account of the patriarchs, for God's gift and his call are irrevocable.

through our gospel 
1 Thessalonians 1:4-5  For we know, brothers and sisters loved by God, that he has chosen you, because our gospel came to you not simply with words but also with power, with the Holy Spirit and deep conviction. You know how we lived among you for your sake.

(parentheses are mine)

Scriptures taken from the Holy Bible, New International Version® NIV®, Copyright© 1973, 1978, 1984, 2011 by Biblica, Inc.® Used by permission. All rights reserved worldwide.