By its own fruit.
Figs are not gathered
Grapes are not picked
From a bramble bush.”
ἕκαστον γὰρ δένδρον ἐκ τοῦ ἰδίου καρποῦ γινώσκεται· οὐ γὰρ ἐξ ἀκανθῶν συλλέγουσιν σῦκα, οὐδὲ ἐκ βάτου σταφυλὴν τρυγῶσιν.
Luke indicated that Jesus continued with his metaphor about fruits. He said that each tree was known by its own fruit (ἕκαστον γὰρ δένδρον ἐκ τοῦ ἰδίου καρποῦ γινώσκεται). Figs are not gathered from thorn bushes (οὐ γὰρ ἐξ ἀκανθῶν συλλέγουσιν σῦκα). Neither are grapes picked or gathered from a bramble or thorn bush. This saying of Jesus was somewhat similar to Matthew, chapter 7:16, perhaps indicating a Q source. There Jesus told his disciples that they would know or discern people by their fruits. Then he asked the question whether grapes could be gathered from thorn bushes or figs gathered from thistles? Certain kinds of fruits only come from certain kinds of trees. Thus, you can tell what kind of tree it is by its fruit. The thorn bushes were not going to produce figs or grapes. What kind of tree are you?