1 Parable of the sower: the Gospel remained the same, but there’re different responses.
2 “although they look they may look but not see, and although they hear they may hear but not understand, so they may not repent and be forgiven.” Why did Jesus not want them to repent and be forgiven? Elsewhere it’s clear that he _does_ want them to repent and be saved… so what’s going on here? In fact, the very next section talks about the parable of the Lamp.
3 Parable of the Lamp: we are to let our light shine. We should not be “undercover Christians”. If nobody knows we’re Christians, something’s wrong. Of course, there’re exceptional circumstances, e.g. in times of severe persecution, but in general this is the case.
4 Parable of the Mustard Seed: Some people interpret it as evil “birds” from the parable of the sower -- but I think more likely it’s talking about how the church from a small beginning grows and spreads to influence the whole world.