Horatius Bonar preaches about the 'Life River' described in Revelation 22:1, emphasizing its significance as a source of spiritual nourishment and blessings. He draws parallels between the earthly rivers of Eden and the heavenly river of life, highlighting its qualities of grace, power, purity, and brightness. Bonar illustrates how this river, flowing from the throne of God and the Lamb, offers eternal life and refreshment to all who partake of it. He encourages believers to seek this river for cleansing and vitality, reminding them of the promise of eternal life and the glory that awaits in the heavenly city.