Great stuff from Steve Wilkins on the Church liturgical year calendar:
"In a sense, the Christian calendar turns the entire year into a drama. Beginning with the Feast of the Incarnation, the world moves progressively from darkness to light. The death of Winter is turned into the resurrection of Spring which corresponds to the Feast of the Resurrection (Easter). Then comes Pentecost and the time of grow and maturity. We do battle with the effects of sin and the curse upon the ground — we fight the weeds and the bugs to protect the seed until the harvest. Now the harvest is coming in and Satan, seeing the defeat of his efforts to destroy us again, seeks one last time to achieve victory before the year’s end. October 31 came to signify that day. Satan seeks to destroy the saints, but he is banished again by the victory of Christ and the joy and gladness that now has filled the earth through the Church."
I would add that the harvest itself (Thanksgiving?) is the symbol of the consummation. Harvest (of souls and offerings) brought in; table set for the Great Feast.
There is more on the true origin of Halloween here, from Pastor Wilkins.