Have you ever considered how many things are held together by nuts and bolts?
Christianity is the same way.
While there are many important doctrines over which Christians disagree, what are the essentials?
Paul gives us the answer:
"Now I would remind you, brothers, of the gospel I preached to you, which you received, in which you stand, and by which you are being saved, if you hold fast to the word I preached to you--unless you believed in vain. For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures, and that he appeared to Cephas, then to the twelve. Then he appeared to more than five hundred brothers at one time, most of whom are still alive, though some have fallen asleep. Then he appeared to James, then to all the apostles. Last of all, as to one untimely born, he appeared also to me." (1Co 15.1-8 ESV)
In short, we have to embrace the same gospel.
Yes, there are different issues that divide Christians' opinions. Calvinist or Arminian? Amillennial or Premillennial? Complimentarian or Egalitarian? Paedobaptism or Credobaptism? Etc.
While these doctrines are important (and they are--let's not kid ourselves with some false ecumenism that sweeps doctrinal differences under the catechizing rug) they are not the crux of the gospel.
What is the crux?
The Godhead is composed of a Trinity of Father, Son and Holy Spirit.
The Son of God, at the Incarnation, became the God-Man and was born of a virgin, Mary.
Jesus Christ lived a sinless life of perfect obedience to Torah.
He died on the cross as a propitiation, an offering of atonement for the forgiveness of the sins of the world (though only those who would believe on his name would receive the provision of forgiveness)*
He body and physically rose from the dead and later ascended into heaven as the victorious Conqueror of Sin.
He sent the Holy Spirit to fill his church.
This is what I believe is of supreme importance; all else, while important, may be disagreed about (and will be)!
*I recognize that some Calvinists will take issue with this statement. Because they believe in Limited Atonement they would say Christ died for the sins of the Elect, not the sins of the World. As a Wesleyan I disagree; however, I do not dispute their salvation even though I take issue with their definition.