Annual Festival Calendar and Its Symbolism
This symbolism helped them transition from the Mosaic Covenant to the New Covenant and grasp the continuity in God's plan of salvation. For these early Christians the feast days (Annual Sabbaths) and weekly Sabbaths took on new meaning in bringing them as the new congregation of God, the Church of God, to the eternal rest in the Kingdom of God.
http://www.bibarch.com/Articles/Festival-Symbolism.htm

Symbols Jesus Used to Explain Himself
Words that correspond to the concepts are totally or partially missing in human conceptual world. As a result these messages are shrouded in symbolic language with the hope that his disciples will be able to grasp its significance as they meditated over his words and teachings.
http://www.acns.com/~mm9n/iam/iam1.htm