So what is this message, that is called a stumbling block to Jews and foolishness to Gentiles; that will cause a division between father and son and brother and sister; that has the power to free the captives and institute the eschaton of Christ's Kingdom that is defined not by Law or ethnicity but by a commonly held faith that identifies us with other believers and as Christ's chosen people?
In 1 Corinthians 15, we see a short statement from Paul about the Gospel. The chapter talks about the bodily resurrection of believers and likens that to the bodily resurrection of Christ which serves as a foretaste of what ours will be like. The historicity of the Resurrection is incredibly important because without that we have no hope as believers (v. 17), because our hope is found in the bodily resurrection and the reality that it really did happen. Paul's words as found in the Scripture are:
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
So much is said that this happened "in accordance with the Scriptures," which refers to the many OT prophecies regarding the person of the Messiah who would come as the Suffering Servant (cf. Isaiah 53, etc.) and would be the propitiation for sin (1 John 2:2). Our hope in the Gospel is found in the fact that it was prophesied about long before the actual event and that it was done as the Scripture said. Our hope in the Gospel is rooted in the truth of Scripture and in it's reliability.
Christ died for our sins - There was a purpose for the death of Christ, He did not get the short straw or a raw deal (Week 1 Chargers vs. Broncos) that led to His innocent death on the cross. No, we see from this that the Savior died for a reason, our sins. On the cross He bore our sins in His body and bore the wrath of God against the thing He hates. The image of sin (man) became the image of the liberation (The God-Man), and in Him our sins can be atoned for because He is the perfect sacrificial Lamb, the sacrifice made once for all.
That He was buried - Jesus' death was really real, contrary to many skeptics who would say that He passed out and woke up and that is why He "resurrected." The description of the Passion, supplemented by our understanding of Roman punishment, and the fact that in His body He took the full wrath of God towards sin (which if you have heard me preach about this I have said that I think Mel Gibson took it easy on Him in the Passion movie). This is the stumbling block to Jews, that the Messiah would die (as a humiliated criminal no less).
That He rose again on the third day - This is the part that we struggle with, that a dead person could come back from the grave. This is the foolishness to the Gentiles, and it is foolishness to many who are in our day. But to us who believe, it is the power of the Hope of the Gospel. It is through this Resurrection that death has been conquered, sin no longer has power. The action taken in the Resurrection was the destruction of the Curse found in Genesis 3. Not only are we forgiven and have God as Father (which is where we stop so often), the Curse that afflicted the whole Creation has been lifted! By conquering death Jesus does what only He could as the Second Adam, to inaugurate a whole new people who are free from this.
It is such a simple message, but it causes people to make several assumptions that because of Sin we are not comfortable making. 1) We do not have the power to fix the problem, 2) We have a problem to start with, 3) There is payment for the problem of sin, 4) Someone else took our punishment, 5) The hope of the universe is found in Christ alone, 6) By aligning with Christ it may cause alienation from others, 7) The key to attaining this is not found in ritual but confession and repentance.
The reason why churches have struggled is that we have gotten away from the simple message of the Gospel and have chosen to dress it up or cater it to the culture instead of preachers standing as prophets in the valley calling for people to repent and draw near to Christ. The mission of the Church is the proclamation of this Gospel message, as preachers we must be faithful to the Word and leave the results up to God. This is a list of affirmations that were put out by a group called "Together for the Gospel" which seeks to reclaim the Gospel in churches and the sufficiency of the Word for the conversion of sinners to repentance and faith in Christ.