Matthew 13:31 (a) This figure represents the great religious group called "the church." It began with a very small group, but has spread all over the earth, and has become a monstrosity. Its members include atheists, idolators and evildoers of every kind. Its branches reach out into every part of society, and in every nation. The birds in this church tree represent evil spirits ruling in church councils. (See also Mark 4:31; Luke 13:19).
Matthew 17:20 (Seed). (a) This figure is used to represent the individual believer. It does not refer to the size of his faith, for the Lord always condemned little faith. Little faith means big doubts. The Lord condemns these. He is telling us that though one may be obscure, unknown, uneducated and unimportant in life, yet if that person is full of faith as the seed is full of mustard, then he may see miracles performed in his life. (See also Luke 17:6).