Persistence, salvation and eternal life assurance: are they compatible?

What is salvation?
A person who is drowning in deep waters is saved from death when he comes to the surface and breaths air.
A slave is saved when he is set free and does not have to honor his former master.
In a certain way, Jesus was saved when the Lord resurrected Him.
We Christians say that a saved person is the one who has eternal life while a lost person is the one who has not.
Who is qualified to be saved?
There are many verses in the Bible talking about that, however we tend to simply put: the one who believes in Jesus.
We forget to pay attention to:
Matthew 24:13 13 But the one who endures to the end, he will be saved.
How, then, may someone be confident that he will endure to the end?
This was my question for a long time. I have seen many people abandoning their faith in Jesus: people that do not congregate in a church, do not read the Bible, do not pray. Perhaps they say to themselves that they are saved, but I am quite sure that under persecution they would not endure to the end because of the great signs that they had already given up their faith.
How can I be different?
In my youth, I also had given up congregating; therefore, I have never been confident on my abilities to follow Jesus.
I have always heard in churches:
- Unless you have assurance of your salvation, you are not saved. If you want to be saved, come and receive Jesus as your savior.
I responded many times to altar calls. I do not know how many times I received Jesus.
For a long time, Matthew 24:13, among many other verses, do not fit to our american model of salvation (quite sure, it is american or, at least, it is British).
Therefore, for a long time, I have seen salvation, endurance and eternal life assurance as not compatible. It took sometime to perceive the root of the incompatibility: free will.
In another post, I will try to be pro free will and then, against free will. I will try to show how it affects our eternal life assurance.

Orchid

My daughter received an orchid as a birthday gift. My wife made her responsible for it, however, she fertilized it and suddenly, the orchid lost their leaves and now it is piratically dead.
My wife is trying to bring it to life again.
I tried to take a lesson from it:
Life is fragile.
She has just discovered that its roots were immersed in plenty water. Certainly our daughter does not know what pleases an orchid. This made me think:
We must respect God's laws to keep life.
The Lord created the human being that was stained by sin. As a sinner, every human must die and every human seems the orchid that is almost dead. How to bring a sinner back to life? The Lord established the way to salvation, as the Lord established how an orchid should live.