As he opens this chapter, Paul's clear purpose is to show that the hope God has placed before us is not based on men's guesses or possibilities, but on the testimony of many eyewitnesses then yet living when he wrote this in the AD 50s. Paul adds that he did not make up the gospel, but it was what he received from Christ, and what he received was exactly the same as what he had later been told by the apostles when he met with them in Jerusalem. Paul is presenting the resurrection of Christ as a historical fact.
We also have available to us the witness of the apostles' lives following the resurrection. Now, people just do not do the things the apostles did without believing what they saw with their own eyes with all their heart. Thus, in the first eight verses Paul reinforces what Peter says in II Peter 1:16-21, that there is plenty of strong evidence of the proof of the resurrection of Jesus Christ. This is not a figment of these men's imaginations. It really did occur, and God did not provide a mere two or three witnesses, but hundreds of them to the fact of the resurrection of the dead.
Paul establishes that our hope is resurrection into the Kingdom of God. However, we must take this hope one step farther if we want to make it a motivating force. The resurrection is, in one sense, merely a promised event given at a point in time. It does not occur merely because we believe it, or even because it has been promised. It occurs because of Who promised it. It occurs because there is a powerful Being of utmost integrity, who cannot lie and who will make it occur. This is where our hope must be, not in what He has promised, but rather Who has promised it. Is our faith in God? So must our hope be in God.