When He says we are sealed with the Holy Spirit until the day of redemption, being the guarantee of our inheritance, He means it.
Not everyone who says to me, Lord, Lord, will enter the kingdom of heaven, but only the one who does the will of my Father in heaven. (Matt. 7:21)
God does not lie. When He says this, He means it.
That does not negate the security of the believer.
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Oh, definitely.
Many Roman Catholics, relying on their rituals, relics, and false works, will not be recognized by Christ. Many in other denominations who go through the motions, but who never had saving faith, will not be recognized.
Have you found the scripture yet that is JESUS telling the mob what IS the will of the Father concerning being saved? It is there in John 6 and has nothing to do with the Eucharist.