In the first volume of The Christian’s Reasonable Service, Wilhelmus à Brakel explains Christ’s office as King as the Mediator of the Covenant of Grace. Christ’s perfection and fulfillment of these roles has implications that the believer can never ignore:

“The kingly office is the third office of Christ. A king is a person in whom alone the supreme authority over a nation is vested. Thus, the Lord Jesus is King, and none but Him. . .

Since the Lord Jesus is King, one must confess Him as such and not be ashamed of Him. "Whosoever therefore shall confess Me before men, him will I confess also before My Father which is in heaven. But whosoever shall deny Me before men, him will I also deny before My Father which is in heaven" (Matt 10:32-33). This must be practiced with discretion, and yet at the same time boldly, willingly, manifestly (and thus without disguise), and in dependency upon the Lord Jesus, persevering therein until death.

Since the Lord Jesus is King, you ought to obey Him. "Hear ye Him" (Matt 17:5); "Beware of Him, and obey His voice" (Exod 23:21). He is the high and lofty One. "Who would not fear Thee, O King of nations? for to Thee doth it appertain" (Jer 10:7). We are placed in subjection to Him. "O Lord, truly I am Thy servant; I am Thy servant" (Ps 116:16). Know Him in His glory, submit yourself at once to Him, approve with delight your obligation to be subject to Him, and offer yourself. Seek to know His will, listen to His answer, and be zealous in your performance.

Since the Lord Jesus is King, you must trust Him, and with confidence consider yourself safe under His protection. Seek no protection apart from Him. "He that dwelleth in the secret place of the Most High shall abide under the shadow of the Almighty. I will say of the Lord, He is my refuge and my fortress: my God; in Him will I trust" (Ps 91:1-2); "Blessed are all they that put their trust in Him" (Ps 2:12). In the Lord Jesus everything is to be found which can bring about rest. He is all-sufficient, omnipotent, good, faithful, and true. To trust in Him is to magnify Jesus in all His perfections. For such there are glorious promises. "They that trust in the Lord shall be as mount Zion, which cannot be removed, but abideth for ever" (Ps 125:1); "Commit thy way unto the Lord; trust also in Him; and He shall bring it to pass" (Ps 37:5).”