1) "But if I tarry long" lean de bradumo) "But if I delay." Paul knew his wish or desire, but he was not certain about God’s will for his itinerary on a daily, weekly, or monthly basis. Like James, he left the leading to the will of God, James 4:13-15; Acts 18:21; 1 Corinthians 4:19.
2) "That thou mayest know" (hina eides) "In order that thou mayest know or perceive." Through written instructions, messages, inspired and found in the Word, men may know helpful things, as they are taught them and perceive them, John 5:39; Acts 17:11; 2 Corinthians 5:10; 1 John 5:13; Romans 8:28.
3) "How thou oughtest to behave thyself" (pos de anastrephesthai) "how it becomes (the) household of God (the church) to behave or deport herself," as well as for Timothy to deport himself, to carry on the work and worship of the church orderly, 1 Corinthians 14:40.
4) "In the house of God" (en oiko theou) "in the household of God." In making, baptizing, and teaching disciples of the Lord, in the church, Ephesians 2:19-22; Ephesians 3:21.
5) "Which is the church of the living God" (hetis estin ekklesia theou zontos) "Which exists as (is) the Church of the continuous living God," an assembly of covenanted, baptized believers, in Ephesus, which was doing the work of God as prescribed, Mark 16:15; Acts 1:8.
6) "The pillar and ground of the truth" (stulos kai edraioma tes atetheias) "The pillar and bulwark or depository of the truth," the support and defense of the Word of God; to whom it was committed, for administration in this Gentile age. This institution is always local in nature and function, never universal nor invisible. One may as well speak of an invisible:
a) Flock, Matthew 26:31-32; Luke 12:32; Acts 20:28; 1 Peter 5:1-4.
b) House or Household, Mark 13:34-35; Ephesians 2:19-22.
c) Temple, 1 Corinthians 3:16-17; Ephesians 2:21-22.
d) Bride, John 3:28-29; 2 Corinthians 11:1-2; Revelation 19:7-9.
e) Kingdom or Government, .
as to speak of an invisible church. The term "the church" is here used in the generic and simply refers to the church as an institution, as to nature and kind, made up or composed of local congregations of literal, visible, baptized, covenanted believers in a specific locality on earth to do God’s work.
"THE CHURCH UNCHANGEABLE"
Look at a river. The exile returns to the haunts of his early years, and there, emblem of peace of God, the river flows as it flowed when his wife was young. Tumbling in snowy foam over the same rock, winding its snake-like way through the same everlasting hills, it rushes through the same verdant meadows, washing the feet of the same everlasting hills, it rushes through the glen with the impetuous passions of a perpetual youth, to pursue its course onward to the ocean that lies glimmering like a silver rim around the land. A gray old man, he seats himself on the bank where wild roses still shed their blossoms on a bed of thyme, and the crystal pool at his feet there, foaming round the old graystone, that bright dancing stream, as they may recall many touching memories of early childhood, and companions dead and gone, seem the same, yet they are not. The liquid atoms, the component parts of the river, have been undergoing perpetual change. Even so it is with the Church of Christ. The stream of time bears on to eternity, and the stream of grace bears on to glory successive generations, while the Church herself, like a river fed by perennial fountains, remains unchangeable in Christ’s immutability, in His immortality, immortal.
--Guthrie