Let’s unpack the Hebrew of dwelling in the secret place.
“Secret place” is in Hebrew, Strong’s H5643, cether, from the three letter primitive root H5641, cather, סָתַר.
Cether (the noun): covering, shelter, hiding place, secrecy; covering, cover; hiding place, shelter, secret place; secrecy (of tongue being slanderous, or backbiting). A hiding, hence, something secret, clandestine, hidden; a veil, covering; protection or defense.
Cather (the verb and primitive root): to hide or conceal; to be hidden or to lie hid.
The root is samech + tav + resh. The ancient Hebrew pictographs paint the picture of the word meaning: the samech is from the thorn, meaning, to grab, hate, or protect. The tav is from the two crossed sticks, meaning, mark, sign, signal, monument. The resh is from the head of a man, meaning, first, top, beginning, man. This is a puzzling combination, but the first usage of words in Scripture is often the definitive usage, and I think that is the case here:
“Behold, thou hast driven me out this day from the face of the earth; and from thy face shall I be hid; and I shall be a fugitive and a vagabond in the earth; and it shall come to pass , [that] every one that findeth me shall slay me.” Gen 4:14 KJV
Cain is remarking on the punishment he received from the Lord, for killing his brother Abel. He was being exiled from his family. His family, moreover, dwelt in God’s face, outside of Eden. Away from God’s face, Cain was saying, he would be visible to every one finding him, who would slay him. So God put a mark (tav) on Cain so that this would not happen.
In other words, thorns (samech) surrounded the marked (tav) man (resh). Now instead of being visible to those who would slay him, he was hidden, camouflaged, behind a hedge of protection (as thorn bushes were used to create a hedge of protection around the flock of sheep at night, to protect them from predators).
This is why pestilence, war, and enemies pass by the Psa 91 man. They cannot see him and are turned back from him, by the wall of thorns. The man is covered and sheltered and hidden from view. So how does one enter in and dwell in this secret place?