"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 4:4-5
One collective body of believers in Jesus
One Spirit, God
One hope and that is through Christ
One Lord over all
One faith because there is only Father God, The Holy Spirit and Jesus
One baptism into that faith
One God who is the Father of all
God is outside of you, in you and works through you
Getting your theology correct is important. Most truths are simple and clearly defined in the scriptures. Most scripture defines itself and does not need an interpreter. I would say that most problems that have to do with religious differences are directly connected to man's unwillingness to read and teach the Word of God in its simplicity. When the scriptures are followed there is no need for extra-biblical preaching and teaching. Pointing everyone to look to Jesus for all their needs to be filled isn't an easy sell in modernity. People would rather be roped into something that has surface pizazz than to find the time to dig deep and find God's message/calling for them. Most people fear the calling of God because they have been taught that they will have to give up everything they once knew, and quit 'this' and start to 'that'.
Leaving denominational differences out of the equation for a moment, God had men, full of the Spirit of God to write down the important components of finding your way to a spiritual life with God. In His wisdom, God left the actual spiritual connection to be made personally between God calling you and you inviting Him into your life/lifestyle. The Bible directs you to the living God. Pastors, priests, evangelists and ministry leaders should all be doing just that. They should be guiding you to a personal relationship with Jesus.
That's where the true action is.
That's where the true power is.
That's where comfort for the soul is found.
That's where strength to go on under awful circumstances comes from.
That's where you will get understanding.
That's where your prayers are answered.
That's where your healing will come from.
That's where wisdom will come from.
That's where you have to go when the bottom falls out.
That's where all the mountaintop experiences are.
Read the verse above real slow. See if you get a sense in your heart that man has really complicated, numerated, extrapolated, expanded, convoluted, confused, obfuscated, muddled, and simply changed, what is clearly, One.