I said this:
"Because we are held by God (Jn 10:28), which is also by grace,
we don't earn losing it by anything we do."
Are you sure that the reference is to abandoning the faith (as opposed to committing sins)?
Neither. Jn 10:28 is about who is holding on to whom. God holds onto His children, obviously. It has nothing to do with conditions, per your questions.
And is that--abandoning the faith--even possible?
Well, let's look at what Jesus said:
"“Those on the rocky soil are those who, when they hear, receive the word with joy; and these have no firm root;
they believe for a while, and in time of temptation
fall away." Luke 8:13
The words "fall away" refer back to "believe for a while". So yes, it is "even possible". Jesus indicated as much.
The obvious meaning of Jesus' words would seem to be that those whom the Father had given him would NOT become faithless.
How is that "obvious"? Please advise. Jesus said nothing about keeping anyone faithful, as your post insinuates. Not even close to that.
Here is exactly what He said: "and I give eternal life to them, and they will never perish; and no one will snatch them out of My hand. My Father, who has given them to Me, is greater than all; and no one is able to snatch them out of the Father’s hand. 30“I and the Father are one.”
Jn 10:28,29
There is nothing here about conditions for not being "snatched" from the Father's hand.
v.28 is a clear statement about eternal security: Jesus gives eternal life to them (believers), and THEY WILL NEVER PERISH. Again, nothing about conditions of behavior. Those who have believed HAVE eternal life. Jesus said that in John 5:24. And again said that they will NOT come into condemnation.