That you cannot lose faith. Read Hebrews and the warnings therein, cautioning them not to backslide falling into unbelief and returning to their old beliefs
Those verses in Hebrews which "on the surface" appear to teach what you are saying don't match your eisegesis once read in context.
Hebrews 3:8-10 says, do not harden your hearts as in the rebellion, In the day of trial in the wilderness, where your fathers tested Me, tried Me, and saw My works forty years. Therefore, I was angry with that generation, and said,
'They always go astray in their heart, and they have not known My ways.' Not descriptive of genuine believers. There is no loss of salvation here. Only a failure to receive it. Verses 18-19 - And to whom did He swear that they would not enter His rest, but to those who did not obey? So, we see that they could not enter in because of
unbelief. That explains the hardened heart. It took them in the opposite direction of God. Considered the truth for a time, then hardened heart and departing from God became their final answer.
*Jude 1:5 - Though you already know all this, I want to remind you that the Lord at one time
delivered his people (the Israelites) out of Egypt, but later destroyed those who did not believe. NOT later destroyed those who stopped believing, but
DID NOT BELIEVE.
Hebrews 3:14 - For we
have become [past tense Greek verb, gegonamen, meaning we have become already] partakers of Christ,
(demonstrative evidence) if we hold fast the beginning of our confidence steadfast to the end. Notice that this is essentially a repeat of verse 6, in which we read: but Christ was faithful as a Son over His house -
whose house we are, (demonstrative evidence) if we hold fast our confidence and the boast of our hope firm until the end.
The wording is not - "and you will become partakers of Christ (future indicative) if you (future indicative) hold fast." It is rather -
"you have been, and now are a partaker of Christ" (demonstrative evidence) if in the future you hold fast the beginning of your confidence steadfast to the end."
Holding fast is proof of genuine conversion.
The point is that not all of these Hebrews have become partakers in Christ and the only ones in the end who will be identified as truly born-again Hebrews who have partaken in Christ, will have been those who have held fast the beginning of their confidence steadfast to the end. Now what about those faltering Hebrews who depart from God, yet begin with loud confidence and profession of loyalty? But then later?
Once again, holding fast is proof of genuine conversion.
Just like in Hebrews 4:1-2, For indeed
the gospel was preached to US as well as to THEM; but the word which they heard did not profit THEM, not being mixed with faith in those who heard it. For
WE who have believed do enter that rest, as He has said: "So I swore in My wrath, 'They shall not enter My rest," although the works were finished from the foundation of the world. *Obviously, not all of these Hebrews were genuine believers. *Notice that verses 2-3 makes a
distinction between US who have BELIEVED and do enter that rest and THEM who heard the word but did not mix faith with what they heard and will not enter that rest because of UNBELIEF.
The experiences in Hebrews 6:4-6 are all preliminary to those decisive beginning stages of becoming a Christian, yet some
draw back to perdition after receiving the 'knowledge' of the truth and do not believe to the saving of the soul, as we see in (Hebrews 10:39). Such people certainly may have experienced sorrow for sin, heard and understood the gospel and have given some assent to it and have become associated with the work of the Holy Spirit while around believers and have tasted the heavenly gift and the powers of the age to come. They may have been exposed to the true preaching of the word of God yet have
simply tasted and stopped there.
In Hebrews 6:9, the writer of Hebrews is speaking to those truly saved (refers to them as
BELOVED). He says that even
though he speaks like this concerning THOSE types of people, He is convinced of better things concerning YOU. Things that ACCOMPANY SALVATION. Thorns and briars and falling away permanently
do not accompany salvation and are not fruits worthy of authentic repentance.
In Hebrews 10:26, the term "sin willfully" carries the idea of deliberate intention which is habitual and
stems from rejecting Christ deliberately. This is continuous action, a matter of
practice. Now we don't walk along our daily life and "accidentally" fall into a pit called sin. We exercise our will but, the use of the participle clearly shows willful, continuous action. The
unrighteous practice sin (1 Corinthians 6:9-10; Galatians 5:19-21);
not the righteous, who are born of God. (1 Corinthians 6:11; 1 John 3:9)
In Hebrews 10:39, we read - But
WE are not
of those who
draw back to perdition, but
OF THOSE who
believe to the saving of the soul. Those who
draw back to perdition do not believe to the saving of the soul and those who
believe to the saving of the soul do not draw back to perdition.
In Hebrews 12:15, we read - See to it that no one
falls short of the grace of God. The NASB reads -
comes short of the grace of God.. The ESV reads -
..fails to obtain the grace of God. Not a loss of salvation here but a
failure to obtain it and not maintain it.