J.C. Ryle introduces his work 'Expository Thoughts on Mark', emphasizing that it is a continuation of his previous volume on St. Matthew, designed to provide practical expositions rather than critical commentary. He aims to assist families in prayer, those visiting the poor, and individual Bible readers, focusing on essential truths for salvation while avoiding minor topics. Ryle acknowledges the challenges of meeting diverse expectations regarding the length of expositions and expresses his hope that this work will lead readers to Christ and deepen their faith. He also reflects on the lack of attention given to the Gospel of Mark by other commentators, asserting its unique value. Ultimately, Ryle prays that this volume will glorify God and encourage readers in their spiritual journey.