On the use of I am in the Gospel of John, see comments at 4:26; for the first use of I am with a predicate, see 6:35. The adjective real first appears in 1:9 in the phrase “real light” (see comments there). In the Old Testament Israel is sometimes spoken of as a vine, and sometimes as a vineyard, and that is perhaps the background of the imagery used in this verse. In these Old Testament passages two emphases are made: (1) Israel’s pure and favored origin, and (2) Israel’s degenerate nature.