They were earnest in asking about that which their Master never had directed or encouraged them to seek. Our Lord knew that his ascension and the teaching of the Holy Spirit would soon end these expectations, and therefore only gave them a rebuke; but it is a caution to his church in all ages, to take heed of a desire of forbidden knowledge.
He had given his disciples instructions for the discharge of their duty, both before his death and since his resurrection, and this knowledge is enough for a Christian. It is enough that He has engaged to give believers strength equal to their trials and services; that under the influence of the Holy Spirit they may, in one way or other, be witnesses for Christ on earth, while in heaven he manages their concerns with perfect wisdom, truth, and love.
When we stand gazing and trifling, the thoughts of our Master's second coming should quicken and awaken us: when we stand gazing and trembling, they should comfort and encourage us. May our expectation of it be stedfast and joyful, giving diligence to be found of him blameless.