What does Mark 4:19 mean?The seed from the sower that lands in a thorn patch will germinate and grow; if the soil is rich enough to nourish thorns, it will nourish wheat. But before long, the weeds will choke the young plant, preventing it from developing mature grain (Luke 8:14). Jesus explains that the seed is someone who hears the gospel and starts to allow it to make changes in their life. But they value worldly riches too much to continue.
The word translated "unfruitful" is from the Greek root word akarpos, and refers to a situation that doesn't bring the results it should. Several characters in the Bible showed this quality. In Mark 10:17–27, the rich, young ruler appears to have spiritual maturity resulting in good works, but the love of his wealth reveals where his heart really lies. One man wants to follow Jesus, but first wishes to bury his father—a one-year-long process; Jesus tells him he has the wrong priorities (Matthew 8:21–22). Herod knows that John the Baptist speaks the truth, but to save face in front of his guests he has John killed (Mark 6:14–29).
It is possible that Jesus' brothers reflect this same belief (Mark 3:21, 31). We aren't told exactly why His brothers want to bring Him back to Nazareth, but it could be that rumors that He was crazy are hurting their business.
Scripture says that "the love of money," not merely money itself, is something which draws us away from Christ (1 Timothy 6:10). We cannot prioritize both money and God (Matthew 6:24). Neither can we focus on earthly comforts if we are called to sacrifice for God's kingdom (Matthew 6:25–33). Jesus points out that it is futile for someone to "gain the whole world and forfeit his soul" (Mark 8:36), whether "the world" means comfort, worldly status, wealth, or even our lives (Mark 8:35).
On a smaller scale, Jesus knows that weeds sometimes invade an otherwise fertile soil where we have resolved to establish deep roots (Matthew 13:24–30). God may leave those weeds—the worldly temptations—because we are where He wants us to be and He can protect us, even in the midst of our enemies (Psalm 23). We need to trust His judgment, allow His word to sink deep into our hearts, and trust that the Holy Spirit will develop fruit (Galatians 5:22–23).