Charles Ellicott Commentary John 3:12

"If I told you earthly things and ye believe not, how shall ye believe if I tell you heavenly things?" — John 3:12 (ASV)

Earthly things—that is, things upon earth, having the sphere of their action upon earth. These are not necessarily restricted to the subjects of this interview. The context includes previous witness borne by Him, and there must have been much which is unrecorded . But the new birth is not excluded from “earthly things,” because it is the entrance to a life which, while it is spiritual, is still a life upon earth.

Heavenly things, in the same way, are things which have the sphere of their action in heaven, the full development of the spiritual life, of which the birth only is on earth; the divine counsels of redemption; the Messianic mysteries, of which this ruler of Israel does not understand even the initiation. Compare to the question in the Wisdom of Solomon, “What man is he that can know the counsel of God? or who can think what the will of the Lord is? ... And hardly do we guess aright at things that are upon earth, and with labour do we find the things that are before us: but the things that are in heaven who hath searched out?” (John 9:13; John 9:16).

The earthly things are the elements of spiritual knowledge, having their test in the moral sense and in their fitness to supply the spiritual needs of humanity. When these elements are learned, the mind is then, and then only, fitted to receive heavenly things. The teaching can only proceed step by step from the known to the unknown; but if the will refuses or the intellect neglects to know the knowable, a person cuts themself off from the power to receive truth. The message from the spirit-world has come, and others read it; but they have not learned the alphabet (Compare to the note on John 16:12).