What the New Testament teaches on this subject is mixed to say the least:
James 2:24 You see that a person is considered righteous by what they do and not by faith alone.
Ephesians 2:8, 9 For it is by grace you have been saved, through faith—and this is not from yourselves, it is the gift of God— not by works, so that no one can boast.
In the early church the biggest advocates of "once saved always saved" were the Gnostics. The church fathers on the other hand taught a Catholic or JW version of salvation that could be lost by wrong action.