Paul and the other apostles all believed and preached the same gospel. Paul did not proclaim a different message from what Peter, James , and the others did (cf. Galatians 2:1-10). This commonly agreed on message is what the Corinthians had believed when those who had ministered in Corinth had preached to them. By denying the resurrection the Corinthians were following neither Apollos, nor Cephas, nor Christ. They were pursuing a theology of their own. [source][source][source]
The point of this section of verses was to present the gospel message, including the account of Jesus Christ"s resurrection, as what many reliable eyewitnesses saw and all the apostles preached. Paul did this to stress that Jesus Christ"s resurrection, which most of the Corinthian Christians accepted, had objective reality, not to prove that He rose from the dead. Even though Paul had a different background from the other apostles, he heralded the same message they did. Consequently his original readers did not need to fear that what they had heard from him was some cultic perversion of the truth. It was the true gospel, and they should continue to believe it. [source][source][source]
Context Summary
1 Corinthians 15:1-11 - The Gospel: Christ Died And Rose Again
If 1 Corinthians 13:1-13 is a psalm of love, this chapter is a psalm of hope-a hope that cannot be ashamed. It is the most memorable argument in existence for the resurrection of the body. We need hardly stay to distinguish between this and the immortality of the soul. The former is distinctly a Christian teaching; the latter has been held by vast numbers outside of the Christian pale.
Notice that the Resurrection was primarily not a doctrine but a fact. It is not necessary to argue it, but simply to say that Christ arose, therefore all will arise, because Christ is the Son of man. Other religions rest on foundations of philosophy and metaphysics, but the empty grave in Joseph's garden is the keystone of the arch. If that cannot be maintained, as it was in the primitive Church, the whole superstructure crumbles like a mass of clouds. But it can be maintained. There is even more evidence for it than for any fact of modern history. Men may as soon refuse to believe in the battle of Waterloo as in our Lord's resurrection. The testimony of Paul is most important, because he knew all that could be alleged or argued against it by the Pharisees. Indeed, he had himself opposed it. Note that the words, not I, 1 Corinthians 15:10, are also in 1 Corinthians 7:10 and Galatians 2:20. [source]
Chapter Summary: 1 Corinthians 15
1By Christ's resurrection, 12he proves the necessity of our resurrection, 16against all such as deny the resurrection of the body 21The fruit, 35and the manner thereof; 51and of the resurrection of those who shall be found alive at the last day
Greek Commentary for 1 Corinthians 15:11
So we preach, and so ye believed [ουτως κηρυσσομεν και ουτως επιστευσατε] This is what matters both for preacher and hearers. This is Paul‘s gospel. Their conduct in response to his message was on record. [source]
Ye believed [ἐπιστεύσατε] When the Gospel was first preached: with a suggestion of a subsequent wavering from the faith. [source]
What do the individual words in 1 Corinthians 15:11 mean?
Greek Commentary for 1 Corinthians 15:11
This is what matters both for preacher and hearers. This is Paul‘s gospel. Their conduct in response to his message was on record. [source]
When the Gospel was first preached: with a suggestion of a subsequent wavering from the faith. [source]