This is a common question. How do I preach doctrine. We have some beliefs as Christians that we need to preach. Doctrines such as the deity of Christ, Salvation by Faith, and perhaps the Trinity.
Related to this are the questions from various tradtions. For example, a Pentecostal asked about preaching on the Gifts including speaking in tongues. An Adventist asked about preaching the Sabbath. A Holiness person wanted to know about preaching on Biblical Holiness.