The Gospel is a very simple message. The core of the message can be fit on one side of an ordinary 8 1/2 by 11 sheet of paper; see the one page tract "The Simple Gospel" at the link below. Salvation involves, essentially, believing a few core facts about Jesus from the heart. The core facts, as Paul stated them, are:
Moreover, brethren, I declare unto you the gospel which I preached unto you, which ye also have received, and wherein ye stand; By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain. For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; And that he was buried, and that he rose again the third day according to the scriptures; And that he was seen of Cephas, and then of the twelve.
I Corinthians 15:1-5
One who truly believes that Christ died for our sins and rose again will call out to him and acknowledge him as Lord:
But what saith it? The word is nigh thee, in thy mouth, and in thy heart: that is, the word of faith, which we preach; That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved. For with the heart man believeth unto righteousness, and with the mouth confession is made unto salvation. For the scripture saith, Whosoever believeth on him shall not be ashamed. For whosoever shall call upon the name of the Lord shall be saved.
Romans 10:8-12, 14
Furthermore, one who truly believes the core message about Christ will "repent"; that is, change his or her mind about the dead works of the pastï¿½and be baptized because of the remission of those sins which Jesus bought:
And Peter said unto them, Repent and be baptized, every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.
Notice, first of all, that the core message is all about Jesus and only about Jesus. It includes us at all only because it declares that He "died for our sins." Thus, it necessarily contains the concepts of sin -- a concept that our culture has largely lost -- and of God's purpose for us, but it contains absolutely no references to our human institutions. It contains no references to any local church, denomination, human organization or doctrinal statement. It is not expressly tied to any set of "orthodox" beliefs about anyone or anything but Christ. This is why Paul could say that he rejoiced even in the preaching of Christ by those who preached him out of envying and strife, because "whether in pretence or in truth, Christ is preached."
Indeed, the core message does not even contain a fully developed doctrine of Christ, but only a belief that he died for our sins and rose again the third day. It does not contain any denomination's pet doctrines. The organized Church has long been guilty of complicating the Gospel by adding to it requirements that a "convert," in order to be recognized as a true Christian and member of the human church organization (concepts often incorrectly equated), must perform certain outward ritual acts and declare his or her agreement with lists of doctrinal positions that are not a part of the core message. The content of these ritual acts and "required" doctrines varies from denomination to denomination, but, in all cases, one underlying purpose is the same: to establish the new believer's loyalty to the organization. There is a place for loyalty tests, but it is not in the initial presentation of the Gospel. The unsaved need to come to Christ, and Christ only, not to the human church organization.
Moreover, the core message about Christ does not, in itself, contain any instructions about what we must do. We must only believe. One who truly believes will call on God, repent and be baptized, but all of these actions, and all of our other steps of obedience, occur subsequently to and as a result of truly believing the core message. This is made clear in the language of the Great Commission itself:
Go, and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all things that I commanded you.
Matthew 28:19-20 (WEB)
Jesus' command to us clearly envisions three separate steps. The first is to "make disciples"; that is, learners, people willing to be taught of all nations. This involves presenting the core message so that the hearer can believe it, change his or her mind (repent) and call on the name of the Lord. Only those who have repented and come into a personal relationship with the Lord by calling on Him can possibly be taught by Him. The second step is baptizing those who have believed. The third step, which must necessarily follow the first, is to teach them everything Jesus has commanded and how to obey it. People who have not believed in Christ and changed their minds about the dead works of their past will have no interest in learning how to obey everything Jesus has commanded. Thus, the first three topics of instruction for new believers, as named by the writer to the Hebrews, are repentance from dead works, faith in God and the doctrine of baptisms. Hebrews 6:1-2. Only when these are established is it possible to teach how the believer ought to live. The organized Church has long made this too complicated by trying to redefine these essential things so as to include its pet doctrines and rituals. But, by doing this, churches have largely limited access to the Gospel to unsaved people with church backgrounds, who already have some knowledge of what is "expected" of them. The Gospel has often been made opaque to unbelievers by our church-friendly additions to it.
Thus, the simple message of the Gospel is that Christ died for our sins, was buried and was raised again the third day according to the Scriptures. Believing the message leads to relationship with God, repentance and baptism, followed by growth. Attendance at church meetings and performance of church rituals are not an essential part of the message. The message of the Gospel is not "please visit our church so you can be saved there." It is all and only a message about Christ.