Those who sow in winter reap in summer. The winter is the world, the summer the other Aeon. Let us sow in the world that we may reap in the summer. Because of this, it is fitting for us not to pray in the winter. That which come out of the winter is the summer. But if any man reap in winter he will not actually reap but only tearing things out, since it will not provide a harvest for such a person. It is not only [...] that it will [...] come forth, but also on the Sabbath [...] is barren.

Philip explains in the second line that the metaphor being used is that winter is the world, or more specifically, the material world and summer is the other Aeon, the spiritual world or spiritual dimensions.  So what Philip is telling us is that we need to prepare for our heavenly life NOW, while we are in the material world.  If we wait until our physical body dies, it's too late.  The next sentence advising not to "pray in winter" seems to contradict that, but I don't think it does.  I think what it means is that praying for material things or to the god of material things does not help us prepare for the afterlife in the spiritual realms.  The next  two sentences agree with that interpretation.  If you "reap in winter" by concentrating your energies on material success and collecting material goods and objects, you are making your short physical life pleasant at the cost of not preparing for and possibly harming your prospects for an eternal life in spirit.