The botanical imagery is that of a successful surgery. A drastic step was taken to save the tree, as step without which "the tree thereof would have perished." In more historical terms, the Lord is indicating that adoption of the gentiles into the Abrahamic covenant was an essential part of the preservation of the promises of the covenant. At this point in the allegory, all is well. As Hoskisson rightly notes, this must refer to the time of Jesus and the decades immediately following (Hoskisson, p. 81).