First, David Warren quoting 14th-century Byzantine emperor, Manuel II Paleologus:
God is not pleased by blood and not acting reasonably is contrary to God's nature. Faith is born of the soul, not the body. Whoever would lead someone to faith needs the ability to speak well and to reason properly, without violence and threats.The whole article is here.
Then, Evelyn Underhill, The Spiritual Life, quoted in the Readings for Reflection in A Guide to Prayer. The three marks of a healthy spiritual life: tranquillity, gentleness and strength.
Finally, from the Sons of Korah, the Psalmists:
The Lord God is a sun and sheild. (Ps 84.11)