What does 2 Timothy 2:19 mean?
Paul has been discussing the importance of holding to sound teaching, especially in the face of false teaching. In particular, he has named certain teachers who are causing a crisis of faith in Ephesus due to their errors. Here, Paul turns to the Old Testament for his source of authority. This "firm foundation" is likely a reference to the Torah. He quotes from Numbers 16:5 in the first citation: "The Lord knows those who are his." Paul affirms that God knows who has truly believed in Christ. False teachers may be persuasive to some people, but not to the Lord.The second Old Testament reference is general, not quoting a specific passage. Most likely, Paul is referring to Numbers 16:26, which best fits the context of this discussion. There, the Israelites were commanded to separate from Korah, Dathan, and Abiram, three men who had rebelled against the Lord. In that story, this separation was meant to be literal and immediate—the wrath of God was about to fall on those insurgents. Separation wasn't just meant to imply disagreement, but to avoid being caught up in the punishment resulting from their sin.
Paul likely had the same application in mind for Timothy, calling him to separate from these false teachers. God would deal with these disobedient ones as He had with others who have rebelled against Him in the past.