The second type of soil which Jesus described was full of rocks. There would have been some good soil, but the heavy stones prevented it from being ploughed without breaking the blade. So the ground became hard and dried out as it was baked in the sun. Stone below the surface prevented any seedling developing an adequate root system. As a consequence, any seed landing on that kind of ground might spring up quickly but be unable to sustain growth to maturity.
 
Jesus was describing hard hearted people who thought that they were open to receive God's Word. They did not understand that beneath the surface, they were resistant to God; even though they were open to religion. Their eagerness for truth was demonstrated by the crowds who followed Jesus wherever He went (Matthew 20:29); but their inner resentment at His authority was seen when they demanded His crucifixion (Matthew 27:20-26).
 
Without roots which tap into underground water, cereal crops cannot survive the blistering sun, chilly nights or violent winds for long. Jesus said that the many different forms of personal trouble, and persecution, would prove overwhelmingly hostile to immature believers. Without deep roots into the truth of God's Word and a living relationship with Him, people cannot grow in God. Religion with all its regulations and pious activity is no substitute.
 
Whenever a believer falls away it is not because of any defect in the gospel, or failure on God's part. They fall away because they are not drinking from a living relationship with Jesus (Isaiah 55:1) and are not tapping into the living water which comes from Him (John 4:14). Trouble comes to everybody; but those who are well watered in truth will be productive in God's kingdom (Psalm 1:3). The trainee apostles needed to understand that although some people seem keen initially but then fall away - the gospel is not defective. So do not get discouraged when shallow believers backslide. Just keep on sowing the seed!