Should political issues be expounded on from the pulpit?
First of all, the Word of God should be expounded on from the pulpit! But that Word sometimes addresses issues that listeners hear as political. For example, God’s Word promotes the sanctity of human life, welcoming strangers, fighting injustice that makes the rich richer at the expense of the poor, and caring for the earth—all of which are also considered political issues today. Should ministers preach about them? Issues some people regard as political to prevent the church from engaging them are what others regard as core kingdom-of-God issues that must be engaged. Perhaps the question should be "How does one preach the full gospel, with all its prophetic applications to our lives, while avoiding partisan politics?"
The Christian Reformed Church Order doesn’t address this in its section about worship, but it does say in Article 28 that the assemblies (councils, classes, and synod) should deal with “ecclesiastical matters only.” Like pastors, sometimes assemblies are accused of being too political. Synod has adopted positions on several issues (crcna.org/welcome/beliefs/position-statements) that many would consider political—abortion, capital punishment, creation care, euthanasia, homosexuality, immigration, race relations, war, and so on. Many of these issues could be considered political by today’s standards but also are core kingdom-of-God matters.
Again, it might be more helpful to use the word “partisan” instead of “political” in discerning what is appropriate for preaching. Avoiding partisan politics would include declining to endorse candidates from the pulpit. In fact, churches should take great care not to violate the requirements of their tax-exempt status as a nonprofit organization by endorsing any political candidates.
Neither the Church Order nor synod has ever listed non-ecclesiastical or political issues that the church should not address. Article 28 mirrors the Church Order adopted at the Synod of Dort in 1619, and in all the years since, the church has discerned the Spirit’s guidance as it deliberates and decides matters. That is the work of the church—discerning how the Word of God speaks in every age. Doing so is bound to involve issues considered political by some from time to time.