Jamieson, Fausset and Brown on Hebrews 6:3

3. will we do--So some of the oldest manuscripts read; but others, "Let us do." "This," that is, "Go on unto perfection."

if God permit--For even in the case of good resolutions, we cannot carry them into effect, save through God "working in us both to will and to do of His good pleasure" (Php 2:13). The "for" in He 6:4 refers to this: I say, if God permit, for there are cases where God does not permit, for example, "it is impossible," &c. Without God's blessing, the cultivation of the ground does not succeed (He 6:7).