Mark 4:14–20 (NKJV): 14 The sower sows the word. 15 And these are the ones by the wayside where the word is sown. When they hear, Satan comes immediately and takes away the word that was sown in their hearts. 16 These likewise are the ones sown on stony ground who, when they hear the word, immediately receive it with gladness; 17 and they have no root in themselves, and so endure only for a time. Afterward, when tribulation or persecution arises for the word’s sake, immediately they stumble. 18 Now these are the ones sown among thorns; they are the ones who hear the word, 19 and the cares of this world, the deceitfulness of riches, and the desires for other things entering in choke the word, and it becomes unfruitful. 20 But these are the ones sown on good ground, those who hear the word, accept it, and bear fruit: some thirtyfold, some sixty, and some a hundred.”
When Jesus told the parable, He said the sower sows the "seed". Here in His explanation He says the sower sows the "word". Jesus has now just interpreted the most important part of the parable. The seed is the word. Now some might ask, who is the sower? If we go back over the events that surround Jesus' ministry around Capernaum, we will remember that He was purposeful about preaching the word. The context shows that He is the sower, and He is sowing the word as He preaches it. But not everyone who hears this word will be effected by it. The parable and the explanation shows unmistakably that all that hear the word receive it with gladness, but not all will keep His word. Satan steals it away from some, others cave in to the cares of the world, and still others to persecution. The only ones that benefit from it are those who hear it, accept it (to come to believe something is true and act accordingly, differing from the word for receive where they lay hold if it, but are not entirely convinced), and bear fruit. Out of all the people that hear Jesus' word, only the last group bears fruit. This is not supplemental to salvation but is part of true salvation. No where in any of the gospels does Jesus teach or accept an empty faith! All those that believe are moved by faith to act. Unlike the modern teaching that all you need to do is say you love Jesus (make a profession of faith), but never change anything in your life to follow Him. We must remember, Jesus said, "by this my Father is glorified, that you bear much fruit; by this you will be my disciples" (John 15:8).