I agree, this is a major point of Christ's message contrary to judaism of the time.
However we should not be complacent, not presume we have God in a box no matter what we do, think or believe; that no matter how much we sin, how many we hurt, whether we believe in God or not, whether we choose to walk with evil, that we need not repent or ask forgiveness; that even if we no longer trust in God, even if we no longer believe in God, He will save us because once we did or thought we did.
It is not an either/or: constant fear or OSAS. Neither is biblical or what Christ taught.
You are absolutely wrong. Once saved, always saved is the foundation of Christ’s sacrifice for us. Period.
The rest of the NT is a road map to show up how we must continue to grow in our walk with Christ. But it repeatedly reminds us that we cannot earn and we cannot keep our salvation through works, deeds, or beliefs. It was a gift to us that cannot be taken away. By anyone. Including ourselves.