This article consists of notes on Lord's Day 31 of the Heidelberg Catechism.

This article stresses the importance of the proclamation of God’s judgment in preaching, as part of the church’s duty to use the keys of the kingdom. The article pays attention to the biblical data, as well as Lord’s Day 31 of the Heidelberg Catechism and the comments of Reformers on the matter.

In this article on Lord's Day 31 of the Heidelberg Catechism, the author shows how the kingdom of heaven is opened by the keys the Lord Jesus himself gave to the disciples. Preaching is the central key is also discussed. The central text is Matthew 16:19.

In this article on discipline, the focus is on all kinds of discipline: self-discipline (self-control), discipline of God, church discipline and also informal church discipline.