The Gospel: 1 Corinthians 15:1-8

1 Now I make known to you, brethren, the gospel which I preached to you, which also you received, in which also you stand, 2 by which also you are saved, if you hold fast the word which I preached to you, unless you believed in vain.  3 For I delivered to you as of first importance what I also received, that Christ died for our sins according to the Scriptures, 4 and that He was buried, and that He was raised on the third day according to the Scriptures, 5 and that He appeared to Cephas, then to the twelve.  6 After that He appeared to more than five hundred brethren at one time, most of whom remain until now, but some have fallen asleep;  7 then He appeared to James, then to all the apostles;  8 and last of all, as to one untimely born, He appeared to me also.
 
Let’s note first of all that Paul is writing to those who received the “good news” from him.  He emphasizes that so that there will be no question about the source or the target of the gospel he preached.  As is true in so many of Paul’s letters, he is repeating for emphasis something that they have already heard from him.  He writes “I make known to you the gospel which I preached to you.”  Then he describes the work of that gospel that has already been done.  He preached it, they received it, and those who stand in it are saved!
Since they are holding fast the gospel message, which he is about to repeat to them, they are those in the church which have been saved.  But he adds the strange phrase “unless you have believed in vain.”  That could mean that their faith is empty, meaningless, and without effect.  Or, it could be a hint as to the reason he is writing this chapter.  After all, if they believed a message of good news concerning a resurrected Savior, but there is no such thing as resurrection and Christ wasn’t raised from the dead, then their faith is in wind … there is nothing to it; that is, it is meaningless.
Then, Paul reviews the contents of the gospel he received (from the Lord) and then preached.  He emphasized that it is of first importance.  It is the foundational message for faith and eternal life, and this is a summary of it.  Notice that the two major aspects of the gospel are the death and resurrection.  Then, Paul gives evidence for each.
First, Christ died for our sins.  He was our substitute, dying to pay the penalty of our sins in our place.  This death was according to (in agreement with) the teachings of the Scriptures (the Old Testament).  When Peter preached on the day of Pentecost, he was very clear that the things that the Jewish leaders and the Romans had done to Jesus had been prophesied long before.
The evidence of His death being real was that He was buried.  The grave was covered with a stone, and a guard was placed there.  The women wondered how they would get to the body of Jesus to anoint Him.  Jesus had truly died.
Then He was raised from the dead on the third day (not Friday, or Saturday, but on Sunday).  His resurrection was also prophesied in the Old Testament (according to the Scriptures).  Jesus, in speaking of His death and resurrection, even spoke of the sign of Jonah who was in the belly of the whale for three days.  Peter emphasized that the Father would not allow His Son to experience corruption.
The evidence of His resurrection is given by referring to those who had “seen” Him after He rose from the dead.  He mentioned Peter, the 12 (a general reference to his disciples, even though Judas had died), 500 brothers at one time (some of whom were still alive, others of whom had already gone to be with the Lord), James (His brother), and all those who were apostles of the Lord (since seeing Jesus was one of the requirements for being an apostle).  Then, finally, Paul mentioned himself, since he saw Jesus on the road to Damascus, and met with Him personally later.  Paul was the last of those who were called apostles and, as we will see, he felt the least qualified because of his life before Jesus stopped and saved him.  
With this clear summary of the gospel, its elements and its evidence, Paul prepared to deal with a false teaching that was troubling some of the believers:  is there, in fact, a resurrection from the dead?  Some who had never seen it were ready to question the possibility, even with all the testifiers and evidence right before them.  Since we live among people who are not willing to believe in miracles, including and especially resurrection – which they have not seen – it is important for us to follow Paul’s argument and be ready to present the good news with faith and power.