Typically, Biblical teaching has been conducted through a singular person committing themselves to on topic or one group of people. Even in small groups, there is a designated leader a lot of the time. When the leader starts to teach, many times it takes the form of a sermon or a lecture. It is quite easy to picture how sermons and lectures could change a life. Gregory of Nazianzus helped solve Christological issues through his theological orations - Augustine was converted through the eloquence of Ambrose's sermons - Charle's Spurgeon affected numerous people through his sermons. To grow the kingdom of God, one can clearly write and give a lecture or sermon.