One of the signs of the genuineness of inspirations, especially extraordinary ones, is peace and tranquility of heart in those who receive them, since the Holy Spirit is indeed powerful, but with a strength that is gentle, mild and peaceful…
On the contrary, the evil spirit is turbulent, bitter and restless. Those who follow his hellish suggestions in the belief that they are heavenly inspirations can usually be recognized because they are unsettled, headstrong and haughty. Under the pretext of zeal, they silence everyone and find fault with everything…In the name of zeal for God’s honor they indulge in the passion of self-love.
— T.L.G. Book 8, Ch. 12; O. V, pp. 100-101