John Calvin on Mark 8:12-21

Mark 8:12. And groaning in his spirit. By these words Mark informs us that it occasioned grief and bitter vexation to our Lord, when he saw those ungrateful men obstinately resist God. And certainly all who are desirous to promote the glory of God, and who feel concern about the salvation of men, ought to have such feelings that nothing would inflict on their hearts a deeper wound than to see unbelievers purposely blocking up against themselves the way of believing, and employing all their ingenuity in obscuring by their clouds the brightness of the word and works of God. The words, in his spirit, appear to me to be added emphatically, to inform us that this groan proceeded from the deepest affection of his heart, and that no sophist might allege that Christ resorted to outward attitudes to express a grief which he did not inwardly feel; for that holy soul, which was guided by the zeal of the Spirit, must have been moved by deep sadness at the sight of such wicked obstinacy.