Thomas Hammerken (or Hammerlein -- both mean "little hammer") was born at Kempen (hence the "A Kempis") in the duchy of Cleves in Germany around 1380. He was educated by a religious order called the Brethren of the Common Life, and in due course joined the order, was ordained a priest, became sub-prior of his house (in the low Countries), and died 25 July 1471 (his feast is observed a day early to avoid conflict with that of James bar-Zebedee the Apostle).
Thomas is known almost entirely for composing or compiling a manual of spiritual advice known as The Imitation of Christ, in which he urges the reader to seek to follow the example of Jesus Christ and to be conformed in all things to His will.
Propers for Thomas à Kempis - Priest, Monk, and Writer
Holy Father, who hast nourished and strengthened thy Church by the writings of thy servant Thomas of Kempen: Grant that we may learn from him to know what we ought to know, to love what we ought to love, to praise what highly pleaseth thee, and always to seek to know and follow thy will; through Jesus Christ our Lord, who liveth and reigneth with thee and the Holy Ghost, one God, for ever and ever. Amen.
The Epistle - Philippians 4:4-9
The Gospel - St. Luke 6:17-23