Paul wrote his letter to the church at Ephesus. The church members had chosen to follow Christ through the preaching of the Gospel and were very young Christians. In what we call Ephesians 3:14-20, Paul tells them how he’s praying for them to grow in their spiritual lives, strengthened by Christ, and their comprehension increased.
He continues in chapter four, earnestly urging them to follow Christ’s example and reminding them they were – and we are – all called for a single purpose.
I therefore, the prisoner of the Lord, beseech you that ye walk worthy of the vocation wherewith ye are called, With all lowliness and meekness, with longsuffering, forbearing one another in love; Endeavouring to keep the unity of the Spirit in the bond of peace. There is one body, and one Spirit, even as ye are called in one hope of your calling; One Lord, one faith, one baptism, One God and Father of all, who is above all, and through all, and in you all. (Ephesians 4:1-6 KJV)
Paul had to address a similar issue within the house of Chloe in Corinth.
Now this I say, that every one of you saith, I am of Paul; and I of Apollos; and I of Cephas; and I of Christ. Is Christ divided? was Paul crucified for you? or were ye baptized in the name of Paul? (1 Corinthians 1:12-13 KJV)
He mentions again that though one might plant and one might water, it is God who provides.
Who then is Paul, and who is Apollos, but ministers by whom ye believed, even as the Lord gave to every man? I have planted, Apollos watered; but God gave the increase. So then neither is he that planteth any thing, neither he that watereth; but God that giveth the increase. (1 Corinthians 3:5-7 KJV)
It is true there are doctrinal differences between denominations, and between churches within denominations. To be called a Christian does require belief of, faith in and service to a single foundation.
For other foundation can no man lay than that is laid, which is Jesus Christ. (1 Corinthians 3:11 KJV)
Cite chapter and verse of God’s word in discussions of doctrinal differences, but to be a follower of Jesus, God’s Messiah, it is necessary to acknowledge Him as the centurion did.
Now when the centurion, and they that were with him, watching Jesus, saw the earthquake, and those things that were done, they feared greatly, saying, Truly this was the Son of God. (Matthew 27:54 KJV)
He did so as Christ died. Surely we can do so knowing of His resurrection? Knowing the church’s one foundation is Jesus Christ, Her Lord?