Monday B-Side
In the parable of the lamp, the lamp is illuminating Gospel truth throughout the world. The Word should be proclaimed, and the light of Christ should shine, openly. The Kingdom will expand, shining God's light to the whole earth. As you share the light of his Word, more will be given to you! As you reject it, more will be taken from you, until you're in outer darkness. He's generous with us so we can be generous with others for the advancement of the Kingdom!
Church growth comes not from man-made programs, but by letting God do the work. We sow the seed, we rest and he does the work.
The harvest, as applied to the apostles and to our mission, can be seen as bringing new converts into the church. Once someone's heart has turned to Christ, we are to usher them into communion with the church body.
The tiny mustard seed growing into a huge tree is naturally impossible, as mustard seeds don't become trees; this shows that the growth of the Kingdom, and the Kingdom itself, is miraculous! As Jesus tells the parable, the Kingdom's beginnings are very humble, a tiny, struggling movement rejected by most people, but it's going to blossom and grow into a massive movement that covers the whole earth!
Jesus' parables were told to give insight to believers, but confound non-believers.