Remember, Paul tells us there is only one gospel. So salvation is the same before the cross as it is after. It mentions this of Abraham and David in Romans 4 and Galatians 1. Yet these 2 were not always obedient. Yet they finished strong.
I assume you talking about the phrase "
shall not enter into my rest"
Psalm 95:11
Unto whom I sware in my wrath that they should not enter into my rest.
Psalm 132:14
This is my rest for ever: here will I dwell; for I have desired it.
Isaiah 18:4
For so the LORD said unto me, I will take my rest, and I will consider in my dwelling place like a clear heat upon herbs, and like a cloud of dew in the heat of harvest.
Isaiah 66:1
Thus saith the LORD, The heaven is my throne, and the earth is my footstool: where is the house that ye build unto me? and where is the place of my rest?
Acts 7:49
Heaven is my throne, and earth is my footstool: what house will ye build me? saith the Lord: or what is the place of my rest?
Hebrews 3:11
So I sware in my wrath, They shall not enter into my rest.)
Hebrews 4:3
For we which have believed do enter into rest, as he said, As I have sworn in my wrath, if they shall enter into my rest: although the works were finished from the foundation of the world.
Hebrews 4:5
And in this place again, If they shall enter into my rest.
The exodus from Egypt has been considered a picture of salvation. Exodus 14:13 shows us this as they were about to cross the Red sea.
And Moses said unto the people, Fear ye not, stand still, and see the salvation of the LORD, which he will shew to you to day: for the Egyptians whom ye have seen to day, ye shall see them again no more for ever.
In my opinion, the idea of entering into His rest, is the key here. Those that crossed the Red Sea were saved from Egypt, but because their lack of faith, they were not allowed into the promise land or "shall not enter into His rest" (Psalm 95:10-11)
I think this pictures the salvation of people that get saved but do not continue in faith. They will be saved from eternal torment, but they will not reign with Christ during the 1000 year millennium.
I believe that to "enter into His rest" means to "reign with Christ".
In other words these verses are referring to the rewards of those that are obedient and that there will be less rewards for those that do not finish strong in their faith. Not about loosing salvation.
And although it is much better than not going to heaven, I think this knowledge that we could have done so much more, may cause many Christians to have a time of regret in Heaven. (maybe some of us can recall disappointing our parents, and how the look of shame that they gave us made us feel)
But not to worry - after this 1000 year millennium, all tears will be wiped away.
(Rev 21:4)
So be sure to Finish your race and finish strong.