Is this (εστιν δε αυτη). Means this. Jesus now proceeds to interpret his own parable.

The seed is the word of God (ο σπορος εστιν ο λογος του θεου). The article with both subject and predicate as here means that they are interchangeable and can be turned round: The word of God is the seed. The phrase "the word of God" does not appear in Matthew and only once in Mark (Mark 7:13) and John (John 10:35), but four times in Luke (Luke 5:1; Luke 8:11; Luke 8:21; Luke 11:28) and twelve times in Acts. In Mark 4:14 we have only "the word." In Mark 3:31 we have "the will of God," and in Matthew 12:46 "the will of my Father" where Luke 8:21 has "the word of God." This seems to show that Luke has the subjective genitive here and means the word that comes from God.