In today's verse, Paul gives us a rather interesting thing to ponder. The Church of the Living God (i.e. the body of believers who belong to Him) is the pillar and ground of truth. To be the pillar and ground of truth is no small task, and thus it is important for us to know what, exactly, it means. So, what does it mean to be the pillar and ground of truth?
Another word that could be applied to us is that we are the stewards of truth (1 Corinthians 4:1; 9:17). We, like the Jews before us (Romans 3:2), have been given the great honour of having God's word declared to us, so that we also may declare it to the world. That is our job as priests (1 Peter 2:9).
Picture a world in which, following the death of the Apostles, the entire Church became very lax in its duties. It never copied the word of God. It never studied it. It never launched mission trips across the world. It never opposed false teachers, or shot down false writings. What sort of world would that be?
The Bible cannot perish, so even if the Church did slack, the scriptures would still be present. Jesus tells us that the very stones can cry out if His people will not (Luke 19:40), and so we can be sure that the scriptures would still exist. But imagining God depended entirely upon the Church, would the scriptures still be preached without us? Would you or I have even heard of them? We would certainly have heard the many false teachings that spread in its place, but without the Church, God would have had to create a better pillar and foundation of truth.
Prior to verse 15, Paul taught Timothy a variety of things. In chapter 3 alone, he explained the qualifications required for being a bishop and a deacon. In verse 14, he says "These things I write to you, though I hope to come to you shortly;", and that is when he delivers the line about how the Church is the pillar and foundation of truth. It is the job of the Church to preserve the truth in a world full of lies. Without us, false teachings spread like wildfire.