The only condition of salvation in the Kingdom is growth. We are to continue to grow from now unto eternity, to become more like God with each passing day. For those whose minds are occupied with the things of eternity it gets easier every day to do the right thing: outwardly we are wasting away, inwardly we are renewed day by day.
He told them another parable: “The kingdom of heaven is like a mustard seed, which a man took and planted in his field. Though it is the smallest of all seeds, yet when it grows, it is the largest of garden plants and becomes a tree, so that the birds come and perch in its branches.
So many of the parables which the Son of Man spoke involved the planting, growing and harvesting of plants. The parable of the mustard seed strongly shows the progressive nature of the Kingdom of Heaven, where the smallest spark of faith can eventually grow in a person to become a great thing. An inconsequential person with little value or status in the eyes of the world can be a great person in the Kingdom.
I personally have witnessed many people who were living on nothing, some even on welfare or disability pension who spent all their waking hours preoccupied with serving God. Though the world sees them as insignificant, they are giving up all their lives for God. For the true believer what the world offers cannot be enough. Living life for mere success is no longer satisfying. The spirit which indwells the child of God compels the believer onward and upward, urging him or her to greater glory and greater service to the our fellow man.
Though we cannot make ourselves grow, we can surround ourselves with the environment which makes growth possible. We can fill up our lives with positive, healthy activities; we can choose to associate with positive, spiritual people; we can spend time in communion with the Father; we can actively pursue the things of the Kingdom and stir up a greater desire to serve others and love God more.