What does Mark 4:5 mean?

As the sower throws seed about his field, some will land on unfertile ground, including thin soil covered by rocks. It's unclear why the plant sprouts and grows so quickly; it may be that the shoot is searching for sunlight beyond the rocks. Without deep soil to grow into, the plant has no choice but to search for nourishment elsewhere. But the thin soil doesn't allow the roots to find water, and the little plant dies in the hot sun (Mark 4:6).

The seed represents the Word of God, and the rocky soil stands for hardship and persecution (Mark 4:17). A great many people look to Jesus as a loving, kind, generous rescuer. They accept His promises quickly and whole-heartedly, but they don't listen to what it is He is saying (Mark 4:9). Jesus does not promise an easy life. In fact, He warns us of persecution (John 15:20). Our faith must not be shallow, like the rocky soil. We must follow Him with a deep character that resolves to absorb everything He has to say (Mark 4:24).

Colossians 2:7 exhorts us to be "rooted" in the word. The word "rooted" is taken from the Greek root word rhizoo and means to be fixed and established. We cannot be firmly rooted if our character is too shallow to value the Word of God. It is bad to have a hard heart that the gospel cannot penetrate, but it's also bad to have a weak nature that rejects the gospel at the first sign of trouble.