I wrestled against the doctrines of "Predestination" and "Election onto Salvation", for around three years, before I finally accepted those verses which support these doctrines, as they are written.
The main ones that troubled me were,
John 15:16 You did not choose Me but I chose you, and appointed you that you would go and bear fruit, and that your fruit would remain, so that whatever you ask of the Father in My name He may give to you.
This verse has both "chosen and appointed", so it caused me some sleepless nights.
2 Thessalonians 2:13-14
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. It was for this He called you through our gospel, that you may gain the glory of our Lord Jesus Christ.
This verse says; "God has chosen you from the beginning for salvation", it goes a step farther by sating that God chose to save the remnant from the beginningh. The idea that man is free to choose God, by using his free will, falls over in the face of these verses.
Then this verse stripped me of all my pride, and I realised I had nothing to boast about. Ephesians 2:8-10 For by grace you have been saved through faith; and that not of yourselves, it is the gift of God; not as a result of works, so that no one may boast.