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.
Arminius On The Sin Against the Holy Spirit is a single chapter work on this issue by James Arminius.
Steele – Love Enthroned is a work on what is love, its different aspects, biblical examples, etc. 23 chs.
In Smeaton – The Doctrine of the Holy Spirit he examines historically what the Bible teaches about the Holy Spirit. This is an old classic work (1862). In the New Testament portion he looks at topics.
Biderwolf-A Help to the Study of the Holy Spirit surveys, names of the Spirit, advent, personality, deity, sealing by, anointing of, fruits, baptism of, filling of, emblems, resistance of the Spirit.
In this 31 chapter (month devotions) book by Andrew Murray (Deeper Life, Dutch Reformed), he examines the spirit of Christ
James Buchanan Office and Work of the Holy Spirit is a reformed work on the work of the Holy Spirit touching on infant baptism and salvation because of parents, etc.