These two verses actually share very little in the Greek and use nouns that are only similar in English.
- 1 Cor 3:9 Θεοῦ γάρ ἐσμεν συνεργοί· Θεοῦ γεώργιον, Θεοῦ οἰκοδομή ἐστε. For we are God's co-workers; you are God's cultivated land, God's house (my translation)
- Matt 13:38 ὁ δὲ ἀγρός ἐστιν ὁ κόσμος· τὸ δὲ καλὸν σπέρμα, οὗτοί εἰσιν οἱ υἱοὶ τῆς βασιλείας· And the field is the world, and the good seed - these are sons of the kingdom … (my translation)
There is are several things to observe about these two accounts:
- Paul uses the noun γεώργιον (georgion) which is a hapex legomenon. It is not an accidental choice. Jesus uses the noun ἀγρός (agros) which occurs about 37 times in the NT.
- Paul is addressing the sanctified, converted saints in Corinth (1 Cor 1:1, 2) and uses two phrases in apposition to describe their calling: a cultivated land (one that had been ploughed and already sown with seed) and God's house. By contrast, in Mark 13 Jesus is interpreting the one of a series of farming parables which each employs the metaphor of soil in a field (not necessarily prepared) to teach about how the Gospel is to be propagated and the difficulties the disciples will face.
BDAG distinguishes between these two words as follows:
- γεώργιον (georgion) = an area of land used for cultivation. In 1 Cor 3:9 it is used as a metaphor of the already established congregation
- ἀγρός (agros) = (#3) arable land outside a village. It is used as a metaphor of people who are yet to receive the Gospel, or the church where there are both good crops and weeds.
The difference is subtle. γεώργιον (georgion from ge land and erg work) literally means "worked land"; while ἀγρός (agros) refers to land whether worked/cultivated or not.
Metaphorically γεώργιον (georgion) refers to people working diligently for the Lord to spread the Gospel; ἀγρός (agros) is used of people more generally, some inside the church (including unfaithful people in the church) and others outside the church to whom the Gospel will be preached.