Cyclopedia of Biblical, Theological and Ecclesiastical Literature
or "Sin against the Holy Ghost" (Matthew 12:31-32. and parallels), appears in the first instance to have been the ascription of the beneficent miracles of Jesus to Satanic power; and it seems to be unpardonable because it argued such an utter perversion of moral sense as to place the person capable of it beyond the province of divine grace. Similar cases of spiritual hardening or judicial blinding are elsewhere referred to in Scripture (Ephesians 4:18-19; Hebrews 6:6). See the Latin monographs on the subject by Dentschmann (Viteb. 1668), Heidegger (Tig. 1675), Fastenau (Hal. 1751), and others cited by Hase, Leben Jesu, p. 152. (See BLASPHEMY); (See SIN).
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McClintock, John. Strong, James. Entry for 'Unpardonable Sin'. Cyclopedia of Biblical, Theological and Ecclesiastical Literature. https://www.studylight.org/encyclopedias/eng/tce/u/unpardonable-sin.html. Harper & Brothers. New York. 1870.