The church indeed is one; the church indeed was founded by Christ; the church indeed are the children of God from Adam to the last at His glorious appearing.
Those who are of His church, who walk in the Spirit “are no longer strangers and foreigners, but fellow citizens with the saints and members of the household of God, having been built on the foundation of the apostles and prophets, Jesus Christ Himself being the chief cornerstone, in whom the whole building, being fitted together, grows into a holy temple in the Lord.” (Eph. 2:19-21)
Paul, having been sent to preach to the Gentiles, laid the foundation of the Gospel of Christ for us to build upon. Paul knew what he had been called to do and he knew it was the work of God in him. Indeed he also knew his letters were inspired by God.
“For this reason I, Paul, the prisoner of Christ Jesus for you Gentiles — if indeed you have heard of the dispensation of the grace of God which was given to me for you, how that by revelation He made known to me the mystery (as I have briefly written already, by which, when you read, you may understand my knowledge in the mystery of Christ), which in other ages was not made known to the sons of men, as it has now been revealed by the Spirit to His holy apostles and prophets: that the Gentiles should be fellow heirs, of the same body, and partakers of His promise in Christ through the gospel, of which I became a minister according to the gift of the grace of God given to me by the effective working of His power.” (Eph. 3:1-7)
We are not saved by simply accepting the Lord Jesus into our hearts. The word is received into a variety of hearts — some like the stone pathway, some like the shallow soil, some like the weed infested ground, and some in the good soil. If the heart that receives the word of God is like the good soil, he will bear fruit beginning with the fruits of repentance. For such a one can echo the inspired words of Paul, who said:
“For I am persuaded that neither death nor life, nor angels nor principalities nor powers, nor things present nor things to come, nor height nor depth, nor any other created thing, shall be able to separate us from the love of God which is in Christ Jesus our Lord.”