Albert the Great On Cleaving to God is a very old work, attributed to Saint Albert the Great. It has 16 chapters.
Plumer William Theology for the People
In this 22 chapter doctrines book, Berkhof (Presbyterian and Reformed) looks at some typical systematic theology themes: Revelation, Scripture, Nature-Names-Attributes of God, the Trinity, Creation, Divine Decrees, Providence, Man, Sin, States and offices of Christ, Salvation and Sanctification.
Cox details the evidence for the doctrine of the Trinity in the Bible looking dozens of different angles.
In this very short 2 chapter work, Austin-Sparks (Deeper Life) presents us with the “horizoned by glory”. To be horizoned by something is to be completely overwhelmed by it.
Anon Basic Christian Doctrine is a 50 Chapter doctrines book that is anonymous.
Robert Shaw’s short 1 chapter work on God and the Holy Trinity is an excellent collection of observations and verses that defend the Trinity.