A very small sampling of wisdom from his classic, The Imitation of Christ:
From Book II "Directives for the Interior Life":
Always take the lowest place for yourself and the highest will be given to you. There is a highest place only because there is a lowest. The saints who are greatest before God are least in their own eyes, and the greater their glory the more humble they are in themselves. Because they are filled with truth and the glory of heaven, they seek no empty glory ...
Jesus today has many lovers of His heavenly kingdom, but few of them carry his cross. He has many friends who ask for consolation, but few who pray for affliction. He has many companions to share His meals, but few to share His abstinence. We all want to rejoice with Him, but few of us are willing to suffer anything for His sake. Many follow Jesus up to the breaking of the bread, but few go on to the drinking of the chalice of His passion.
From Book III "On Interior Consolation":
Blessed are the ears that are attuned to God's quiet whisper, and ignore the world's raucous sounds.
If I am only outwardly admonished and not interiorly set on fire I may die and find that my life was without fruit, and at the moment of judgment I may be condemned for hearing the word but not fulfilling it, for knowing it but not loving it, for believing it but not living it.