Christ did not decline the title of king when it was applied to Him in irony (John 18.37), and only explained that His kingdom was not of this world. Even in the state of humiliation, He exercised royal functions. He called to Him whom He would, and they came (Mark 3.13) and, as it was the office of the Jewish king to represent and maintain the unity of the body politic, so Christ, before He ascended, laid the foundation of the visible church, choosing apostles, ordaining outward tokens of church membership (Matthew 28.19; 26.27-29), conferring powers for the exercise of discipline (Matthew 18.15-19), and promising His presence with such societies to the end of time.
But, with His ascension, the plenary exercise of the regal office commenced. It must not be confounded with the dominion which, as the Logos, He exercises over all creatures. The power which is now given to Him in heaven and on earth is for mediatorial purposes and dates from the ascension.
From: Introduction to Dogmatic Theology by Edward Arthur Litton; fourth edition, edited by Philip E. Hughes (London: James Clarke & Co., Ltd., 1960), p. 237. This fourth edition is a revision of the third edition of 1912. The book was originally published in two volumes in 1882 and 1892.