And the soul that turneth after such as have familiar spirits, and after wizards, to go a {d} whoring after them, I will even set my face against that soul, and will cut him off from among his people.

(d) To esteem sorcerers or conjurers is spiritual whoredom, or idolatry.Leviticus 20:6 Parallel Commentaries

Self-Denial.
"If any man will come after Me, let him deny himself, and take up his cross, and follow Me."--Matt. xvi. 24. Good works are not the saint's sanctification, any more than drops of water are the fountain; but they spring as crystal drops from the fountain of sanctification. They are good, not when the saint intends them to be good, but when they conform to the divine law and proceed from a true faith. Yet the intention is of great importance; the Church has always taught that a work could not be called …
Abraham Kuyper—The Work of the Holy Spirit

Epistle Lxiv. To Augustine, Bishop of the Angli .
To Augustine, Bishop of the Angli [174] . Here begins the epistle of the blessed Gregory pope of the city of Rome, in exposition of various matters, which he sent into transmarine Saxony to Augustine, whom he had himself sent in his own stead to preach. Preface.--Through my most beloved son Laurentius, the presbyter, and Peter the monk, I received thy Fraternity's letter, in which thou hast been at pains to question me on many points. But, inasmuch as my aforesaid sons found me afflicted with the …
Saint Gregory the Great—the Epistles of Saint Gregory the Great

Leviticus
The emphasis which modern criticism has very properly laid on the prophetic books and the prophetic element generally in the Old Testament, has had the effect of somewhat diverting popular attention from the priestly contributions to the literature and religion of Israel. From this neglect Leviticus has suffered most. Yet for many reasons it is worthy of close attention; it is the deliberate expression of the priestly mind of Israel at its best, and it thus forms a welcome foil to the unattractive …
John Edgar McFadyen—Introduction to the Old Testament