And, Paul in defending his teachings of resurrection uses a first century practice of 'baptizing for the dead' which according to him is totally ok because of the underlying belief. Paul asks:
1 Cor 15:
29 Now if there is no resurrection, what will those do who are baptized for the dead? If the dead are not raised at all, why are people baptized for them?
30And as for us, why do we endanger ourselves every hour?
We can easily tell that this group's practice does not stem from the idea that resurrection is miles in the future (21st century and counting), they believed that resurrection was first approaching and in their life time (before they died) and they baptised people in the name of old saints like Abraham/ Jacob/ Isaac/Moses believing that these saints will resurrect and indwell and guide them - more like Catholics, only difference is that Catholics baptize young ones.
And Paul is asking, if there's no resurrection, what will they do? they were just wasting there time if there was no resurrection. Paul is saying, they did not waste their time because resurrection is a fact, not a future fact but a continuous one from some point in the late 1st century.