A.T. Robertson Commentary Revelation 7:3

"saying, Hurt not the earth, neither the sea, nor the trees, till we shall have sealed the servants of our God on their foreheads." — Revelation 7:3 (ASV)

Hurt not (μη αδικησητε). Prohibition with μη and the ingressive aorist active subjunctive of αδικεω, not to begin to hurt.

Till we shall have sealed (αχρ σφραγισωμεν). Temporal clause of indefinite action for the future with αχρ (sometimes αχρις ου or αχρις ου αν) and the aorist subjunctive as in 15:8; 20:3,5 or the future indicative (17:7), usually with the notion of ascent (up to) rather than extent like μεχρ.

An (modal) sometimes occurs, but it is not necessary. But there is no futurum exactum idea in the aorist subjunctive, simply "till we seal," not "till we shall have sealed."

Upon their foreheads (επ των μετωπων). From Eze 9:4. Old word (μετα, ωπς, after the eye, above the eye, the space above or between the eyes), in N.T. only in the Apocalypse (7:3; 9:4; 13:16; 14:1,9; 17:5; 20:4; 22:4). For "the servants of God" (τους δουλους του θεου) who are to be thus marked linked with angels in the service of God see Re 1:1; 2:20; 19:2,5; 22:3,6.