At the core of reformed theology there is been a deepening understanding of what has been commonly know as Calvinism or the acronym, TULIP.
Total Depravity – 1 Corinthians 2:14 – Mark 7:21-23 – Romans 6:20
Unconditional Election – Ephesians 1:4-5 – Ephesians 1:5 – Romans 8:29
Limited Atonement – Matthew 1:21 – John 10:11 – John 11:51-52
Irresistible Grace – John 6:44 – Ephesians 8:28 – Acts 13:48
Perseverance of the Saints – John 10:28 – Philippians 1:6 – Romans 11:29
These are the doctrines have been at the core of faithful Christian belief for centuries. However, it is best not to not put them squarely in any denominational camp, Many have taken to calling the the Doctrines of Grace. This is an apt description being that is what they are, Gods grace.
Ephesians 2:8-9 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.
Before the reformation these doctrines were confirmed as being biblically understood. As far back at 60 AD there are quotes from early church fathers espousing this understanding of the scriptures. https://www.apuritansmind.com/arminianism/calvinism-in-the-early-church-the-doctrines-of-grace-taught-by-the-early-church-fathers/