Let me try to answer the title question by first explaining that for assurance of salvation a person must be correct about the facts of the Gospel. The apostle John tells us the reason for his writing his first letter, “These things I write to you who believe in the name of the son of God, so that you might know you have eternal life.” (1 John 5:13) In order for any person to know they have eternal life, they must know that what they know is the absolute truth. No one can believe a lie and receive eternal life because the person who believes and is saved must believe the truth.
This then posses a certain problem or a complexity about learning hereafter. No one who comes to an assurance of salvation wants to think they can be wrong about what they believe, since what they believe is the reason they are saved. Paul said, “For I am not ashamed of the Gospel, for it is the power of God for salvation to everyone who believes…” (Romans 1:16) The problem that arises for the believer is the necessity in his mind that he is right about facts of the Gospel. However, no believer is right about everything because not everything believed is necessary for salvation.
The thing that is necessary for the person who wants to remain teachable is a clear understanding of what facts are necessary for salvation. Those facts that are not necessary for salvation, and do not compromise the Gospel, nor give cause for another person to stumble into sin are negotiable. That is, there is room to be wrong about such teachings that do not fall into the previously mentioned categories.
Teach-ability is a very necessary characteristic because the person that is not teachable is not humble. Those who are not teachable believe themselves to be right about everything.; no one who believes himself to be right about everything is humble. Humility is an absolute necessity for anyone who wants to walk with God. “Therefore it says, “God is opposed to the proud, but gives grace to the humble.” (James 4:6) No one walks with God who also causes God to resist him.
As we go through the letter to the Romans it will become completely clear what teachings are necessary for salvation. There is no book in the New Testament that teaches the Gospel so completely as the letter to the Romans. No one who regards the Bible as truth from God wants to be wrong about any teaching therein. However, if we would be honest about ourselves and continue to learn as we go through life, we must remain teachable.