Can Christians Lose Their Salvation?

Whether they call it eternal security, perseverance of the saints, or once saved, always saved, many Protestants believe that once a person enters into a saving relationship with Jesus Christ, that they can never lose their salvation. And there are Bible verses that DO seem to say that if you read them a certain way. But if this is what the Bible really teaches, why didnt the early Christians seem to know about this teaching? And why do so many Christians today read the Bible as denying eternal security?

Chapters
0:00 - Intro
0:09 - Overview
2:05 - Red flags
8:16 - Pipers answer
15:27 -The Greek to call
18:17 - No Security readings
19:18 - Gods faithfulness, not ours
20:49 - External threats to salvation
24:30 - Implicit Conditionality
28:07 - A case against security
37:20 - Scripture and deadly Sin
41:12 - Biblical examples of mortal sin
47:05 - Hebrews and sin
58:21 - Eternal security and apostasy