How do we know that Old Testament saints were saved the same way as New Testament saints?

The New Testament teaches that there is fundamentally no different means of salvation between Old Testament and New Testament believers. As seen in Acts 1:5 and throughout Scripture, both groups look to Christ for their salvation. Old Testament saints, such as Abel and Enoch, were saved by faith in the coming Messiah, just as we are saved by faith in the Messiah who has come. This unity in salvation underscores that all believers are elected by God, as stated in Ephesians 1:4-5, and regenerated by the Holy Spirit, allowing them to believe in Christ for salvation. Thus, the process of belief has always required the work of the Holy Spirit, whether in the Old or New Testament.