The Pursuit of God by A.W. Tozier is available free at The Project Gutenberg

Here is a masterly study of the inner life by a heart thirsting after God, eager to grasp at least the outskirts of His ways, the abyss of His love for sinners, and the height of His unapproachable majesty—and it was written by a busy pastor in Chicago! (Samuel M. Zwemer)