A.T. Robertson Commentary Matthew 13:38

"and the field is the world; and the good seed, these are the sons of the kingdom; and the tares are the sons of the evil [one];" — Matthew 13:38 (ASV)

The field is the world (ο δε αγρος εστιν ο κοσμος). The article with both "field" and "world" in Greek means that subject and predicate are coextensive and so interchangeable. It is extremely important to understand that both the good seed and the darnel (tares) are sown in the world, not in the Kingdom, not in the church. The separation comes at the consummation of the age (συντελεια αιωνος, 39), the harvest time. They all grow together in the field (the world).