Mark 4:26-29 He also said, "This is what the kingdom of God is like. A man scatters seed on the ground. Night and day, whether he sleeps or gets up, the seed sprouts and grows, though he does not know how. All by itself the soil produces grain-- first the stalk, then the head, then the full kernel in the head. As soon as the grain is ripe, he puts the sickle to it, because the harvest has come." ( NIV)
In the parable of the sower, the seed represented the Word of God. Once this is sown in one's heart or in others, it grows into convictions and applications which make one's faith of a quality acceptable to God for salvation and develops one's character to become more Christlike. But this growing process is not accomplished purely by the sower. God himself works behind the scenes doing most of the work. The Apostle Paul was such a sower and he writes:
"I planted the seed, Apollos watered it, but God made it grow. So neither he who plants nor he who waters is anything, but only God, who makes things grow." 1Cor 3:6,7
So let not ministers of the gospel, or anyone else, attribute such growth purely to their own efforts, or take credit for what God has accomplished. Nor should we give too much credit to "spiritual leaders", which often results in divisiveness in the Christian community, which is the context of Paul's statement in 1Corinthians 3.
But another application is that it doesn't really take much effort to experience fruitfulness. Jesus can take our five loaves and two fish and multiply them to feed thousands. Let this be a reminder to those claiming not to have much time available for ministry. Just do a little and see the results. Once you've eaten of the first harvest, you'll be more experienced and motivated to do more.