Yea, though I walk through the valley of the shadow of death, I will fear no evil: for thou art with me; thy rod and thy staff they comfort me. Yea, though I walk through the valley of the shadow of death - The reference is still to the shepherd. Though I, as one of the flock, should walk through the most dismal valley, in the dead of the night, exposed to pitfalls, precipices, devouring beasts, etc., I should fear no evil under the guidance and protection of such a Shepherd. He knows all the passes, dangerous defiles, hidden pits, and abrupt precipices in the way; and he will guide me around, about, and through them. See the phrase shadow of death explained on Matthew 4:16 (note). "Thof I ward well and imang tha, that nouther has knowyng of God, ne luf or in myddis of this lyf, that es schadow of ded; for it es blak for myrkenes of syn; and it ledes til dede and il men, imang qwam gude men wones: - I sal nout drede il, pryve nor apert; for thu ert with me in my hert, qwar I fele thu so, that eftir the schadow of dede, I be with the in thi vera lyf." - Old Psalter.
For thou art with me - He who has his God for a companion need fear no danger; for he can neither mistake his way, nor be injured.
Thy rod and thy staff - שבטך shibtecha, thy scepter, rod, ensign of a tribe, staff of office; for so שבט shebet signifies in Scripture. And thy staff, ומשענתך umishantecha, thy prop or support. The former may signify the shepherd's crook; the latter, some sort of rest or support, similar to our camp stool, which the shepherds might carry with them as an occasional seat, when the earth was too wet to be sat on with safety. With the rod or crook the shepherd could defend his sheep, and with it lay hold of their horns or legs to pull them out of thickets, boys, pits, or waters. We are not to suppose that by the rod correction is meant: there is no idea of this kind either in the text, or in the original word; nor has it this meaning in any part of Scripture. Besides, correction and chastisement do not comfort; they are not, at least for the present, joyous, but grievous; nor can any person look forward to them with comfort. They abuse the text who paraphrase rod correction, etc. The other term שען shaan signifies support, something to rest on, as a staff, crutch, stave, or the like. The Chaldee translates thus: "Even though I should walk in captivity, in the valley of the shadow of death, I will not fear evil. Seeing thy Word (מימרך meymerach, thy personal Word) is my Assistant or Support; thy right word and thy law console me." Here we find that the Word, מימר meymar, is distinguished from any thing spoken, and even from the law itself. I cannot withhold the paraphrase of the old Psalter though it considers the rod as signifying correction: "Sothly I sal drede na nylle; for thy wande, that es thi lyght disciplyne, that chasties me as thi son: and thi staf, that es thi stalworth help, that I lene me til, and haldes me uppe; thai have comforthed me; lerand (learning, teaching) me qwat I suld do; and haldand my thaught in the, that es my comforth."