Whether you are giving or receiving comfort, these books will equip through hard times. (ranked in the order I’d recommend reading them).
The Wonderful Works of God by Herman Bavinck (condensed version of Bavinck’s four-volume Reformed Dogmatics)
The Institutes of the Christian Religion (1541 edition) by John Calvin
Knowing God by J.I. Packer
The Christian Life by Sinclair Ferguson
The Expulsive Power of a New Affection by Thomas Chalmers
The Pearl of Christian Comfort by Petrus Dathenus
Cultivating Epiphanies 