Please, if you will, clearly underline where Paul said we could not leave Christ in Ephesians 1:13-14. I am really not seeing anything that says that.
First, thanks for asking, so we can have a discussion of the meaning of these important verses.
Here are the 2 verses, with emphasis on the red words:
13 And you also were
included in Christ when you heard the message of truth, the gospel of your salvation.
When you believed, you were marked in him with a seal, the promised Holy Spirit,
14 who is a deposit guaranteeing our inheritance until the redemption of those who are God’s possession—to the praise of his glory.
So, first, Paul says of those who have believed, are "included in Christ". Then he said they "were marked in Him with a seal, the Holy Spirit. Then he explained that the indwelling Spirit "is a deposit". Then he said this deposit "guarantees our inheritance". Then he explained what this sealing with the Spirit is for: "until the redemption of God's possession".
If it were possible for anyone so sealed can be "excluded from being in Christ", where are there no verses? None of the farming metaphors regarding branches in fire relate because Paul never related them. Paul wasn't using metaphors here.
So, please explain how a guarantee isn't really a guarantee, or under what conditions, within this context, can a guarantee be revoked.
He plainly said our inheritance is guaranteed for the day of redemption. What was he referring to, if not eternal security?
Gal 1:6-7
I am astonished that you are so quickly deserting him who called you in the grace of Christ and are turning to a different gospel—not that there is another one, but there are some who trouble you and want to distort the gospel of Christ.
I do know that some distort the Gospel of Christ - which astonished Paul that some would desert God turning to it. So, Paul very clearly states it is possible, and actually calls some out for doing so.
Again, there is no argument, from me anyway, that a person can desert God in the sense of ceasing to believe in Him, or follow Him.
What I disagree with is that ceasing to believe in Him or ceasing to follow Him can result in loss of salvation. There just aren't any verses that say so. And I've explained what Eph 1:13,14 say.
If you desert Christ, you leave the seal that He provides.
1Jo 5:11-12
And this is the testimony, that God gave us eternal life, and this life is in his Son. Whoever has the Son has life; whoever does not have the Son of God does not have life.
Well, these verses certainly DO NOT say what you're claiming.
So, what verses DO say what you're claiming?
John said nothing about deserting Christ, or anything about the "seal" that Paul spoke of.
So your claim has no substance, from these verses, at least.