Thank you for your question about 1 Timothy 3:15: " But if I tarry long, that you may know how you ought to behave yourself in the house of God, which is the church of the living God, the pillar and ground of the truth."  In verses 1-14 of chapter 3, the Apostle Paul had listed the qualifications for a man to be considered for service 1) as an overseer (elder) or 2) as a deacon (assistant) in the church.  In verse 15, he said that he wrote this before he was to arrive so that Timothy would know how to conduct the  election of servants in the church. 

The key points of 1 Timothy 3:15 involve the WHOLE house of God, the church, not just overseers or deacons.

What does the phrase "house" mean?  It comes from the Greek word "oikos" which means a literal or figurative dwelling, implied as a family home.  The early Christians met in homes and addressed one another as "brother" or "sister" as in a family.  Throughout time, groups of Christians have met and continue today to meet together in smaller groups to study God's word, the Bible, just as the noble Bereans studied daily in Paul's time.  Acts 17:11:  "…these [Bereans]…searched the scriptures daily, whether those things were so."

So the focus is on "house" as a figurative grouping of Christians who study and worship together, not a literal building.

What Greek word is translated "church" in this text?  The Greek word "ecclesia," translated "church," means "called out ones."  It harmonizes with the idea of local smaller groups which worship together, led by overseers and deacons, just as Paul explained in the previous verses. "Church" or "ecclesia" does not mean an organization that has several layers of authority – these are made by man, and not authorized by Scripture.

1 Timothy 3:15 ends with the thought that the "house of God," which is "the church of the living God" – the groups of sincere worshippers – are the "pillar and ground of the truth."   HOW do these sincere worshippers become both the pillar and the ground of the truth? This is made clear in 2 Timothy 2:15:  "Study to shew yourself approved unto God, a workman that needs not to be ashamed, rightly dividing the word of truth." 

  1. By diligently studying God's word, sincere students are "the pillar" of the Church.  They are strong and support the church because they have examined Scriptures, reasoned through Scripture so that they can understand Scriptural teachings and harmonize various Scriptures. 
  2. Thus, having studied diligently, they have laid the foundation or "the ground," for understanding what is the true meaning of Scripture, "the truth." 

Paul's inspired words are as relevant today as they were in his day.  The church of God uses his guidelines for their organization, and sincere believers study Scriptures carefully to learn the meaning and truths found in them.