That’s not very difficult. Here is the verse: “…but in case I am delayed, I write so that you will know how one ought to conduct himself in the household of God, which is the church of the living God, the pillar and support of the truth.”
Paul was writing a letter to Timothy, which was the very word of God, and he told Timothy the reason he was writing it was so Timothy would know what God expects of a Christian in the Church. So it is Scripture that is our source for knowing God’s will. And then he says that the church (literally, “the called-out ones”) of the living God is the pillar and support of the truth. The Church is a habitation that God lives in. It is a structure made up of all believers through the ages–all truly saved people. Jesus is the foundation. In Ephesians Paul says it is “built on the foundation of the apostles and prophets, Jesus Christ Himself being the Chief Cornerstone” Here Paul says the church is a pillar of that foundation. In this world, it is the Church (as defined above) that upholds the truth. We believe it, proclaim it, wrote it, live it. but the truth itself is in the Scriptures, which of course center in Jesus. So that’s a great verse all Christians embrace.
At first I thought you were talking about II Timothy 3:15. Here it is–“and that from childhood you have known the sacred writings which are able to give you the wisdom that leads to salvation through faith which is in Christ Jesus.”