Exegesis:

to de en tē kalē gē ‘but that (which is) in good soil.’ Same structure as in v. 14.

houtoi eisin hoitines en kardia kalē kai agathē akousantes ton logon katechousin ‘they are those who, having heard with a good and true heart, keep the word.’ The phrase en kardia kalē kai agathē goes either with akousantes (cf. New English Bible), or with katechousin (cf. Revised Standard Version), preferably the former because of its place immediately before akousantes. en has here instrumental meaning. kalē and agathē may perhaps be interpreted as reinforcing each other and rendered ‘truly good’ (cf. Grundmann).

katechō here ‘to keep,’ of the Gospel message, as in 1 Cor. 11.2; 15.2; cf. Heb. 10.23.

karpophorousin en hupomonē ‘they bear fruit with patience.’ karpophoreō.

hupomonē ‘patience,’ ‘perseverance,’ ‘constancy,’ especially in trial and tribulation (cf. 21.19). en hupomonē refers to the attitude of him who bears fruit.

Translation:

Hearing the word, hold it fast in an honest and good heart, preferably, ‘hear the word in an honest … heart, and hold it fast.’ The prepositional phrase gives to the hearing a deeper meaning, indicating the heart as the means for considering and assimilating what is heard. To hold fast, i.e. to retain faithfully, to keep and obey. Honest and good, a pair of closely synonymous adjectives; hence, ‘truly/really/very good,’ cf. also “in the true goodness of their hearts” (The Four Gospels – a New Translation).

Bring forth fruit, or, ‘bear fruit,’ or non-metaphorically, ‘produce results.’

With patience, or, “by their perseverance” (New English Bible), ‘because they have held through’ (Sranan Tongo), and with a further shift, “persist until they bear fruit” (Good News Translation). Patience in the sense of ‘perseverance,’ ‘steadfastness’ has been rendered, ‘firmness/toughness of heart’ (Bahasa Indonesia RC, Tae’), or by an expression built on ‘brave’ (Marathi).

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.