The Pure in Heart
This passage deals with a spiritual state similar to the fear we feel when our hearts are dark and confused, and it emphasizes the spiritual battle believers must fight every day. Just as a beautiful view cannot be seen through a dirty window, if a believer's heart is not clean, it is hard to grasp God's glory and love clearly. So we need the training of brushing off the cobwebs of worldly worry and greed and of overcoming ourselves, and this means that faith has matured beyond mere goodness.
The sermon warns that words and actions shape character, and that a single mistake can bring down trust built up over time. Believers must gain gentleness and sound judgment through the training of putting God's word at the center and laying down their own thinking, and this is conduct that matters enough to expand or tear down the kingdom of God. A process of purifying a sinful heart through hardship and refining is also needed, and this is an essential condition for being faithful according to God's law rather than the world's standards, and for receiving the reward of eternal life.
In light of the words, blessed are the pure in heart, for they shall see God, the sermon asks how believers should purify their hearts and live pure lives.