The Father loveth the Son - This authority he traces to the love which the Father has for him - that special, ineffable, infinite love which God has for his only-begotten Son, feebly and dimly illustrated by the love which an earthly parent has for an only child.
Showeth him - Makes him acquainted with. Conceals nothing from him. From apostles, prophets, and philosophers no small part of the doings of God are concealed. From the “Son” nothing is. And as God shows him “all” that he does, he must be possessed of omniscience, for to no finite mind could be imparted a knowledge of “all” the works of God.
Will show him - Will appoint and direct him to do greater works than these.
Greater works than these - Than healing the impotent man, and commanding him to carry his bed on the Sabbath day. The greater works to which he refers are those which he proceeds to specify - he will raise the dead and judge the world, etc.
May marvel - May wonder, or be amazed.