More revisionism in the Insight book. This WT has the article about grasping the meaning and discusses the mustard grain in Matt 13:31,32. It describes the birds. If you look back through the publications, the birds went through a change in meaning from 'enemies of the Kingdom', 'the wicked one' to 'righthearted ones'.
Man's Salvation, 1975 says: "Whom did he explain those “birds” to be like? “The wicked one,” “the Devil.” That is to say, the earthly agents of the wicked Devil."
This remained until 2008, (w08 7/15 p. 18 par. 8): "These birds do not represent enemies of the Kingdom who try to eat up the good seeds, as was true of the birds in the illustration of the man who scattered seed on different kinds of soil. (Mark 4:4) Rather, in this illustration the birds represent righthearted ones who seek protection within the confines of the Christian congregation. Even now, these ones are protected from the spiritually defiling habits and unclean practices of this wicked world."
Interestingly, the Insight book under "Illustrations" on page 1179, says:
The mustard grain was tiny and so it could be used to designate anything extremely small. (Lu 17:6) When fully developed, some mustard plants actually attain a height of 3 to 4.5 m (10 to 15 ft) and have sturdy branches, thus virtually becoming “a tree,” as Jesus said. We are helped to identify the “tree” if we take note of the fact that the series of illustrations in which this one is included was introduced at Matthew 13:13-15 by a statement regarding a negative factor. It should also be noted that in the context “birds” are referred to in a negative sense; they are shown to represent “the wicked one.”—Mt 13:4, 19; Lu 8:12. (WT Library CD 2013 Edition, Insight book, Illustrations, p. 1179)
The Insight book on wol.jw.org changes this:
The mustard grain was tiny and so it could be used to designate anything extremely small. (Lu 17:6) When fully developed, some mustard plants actually attain a height of 3 to 4.5 m (10 to 15 ft) and have sturdy branches, thus virtually becoming “a tree,” as Jesus said. In a comparable way, the Christian congregation started in a very small way on Pentecost 33 C.E. But in the first century, it grew rapidly, and in modern times, the branches of the mustard “tree” have expanded to beyond expectations.—Isa. 60:22. (Watchtower Online, Insight book, Illustrations)
Just thought you'd like to be aware of this. Apparently, they are editing multiple subjects in the Insight book. If you have your hard copies, keep them.