A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
psa 64:1A prayer for deliverance from cunning and malicious enemies, with a confident view of their overthrow, which will honor God and give joy to the righteous. (Psa 64:1-10)
preserve . . . fear--as well as the danger producing it.
psa 64:2insurrection--literally, "uproar," noisy assaults, as well as their secret counsels.
psa 64:3Similar figures for slander (Psa 57:4; Psa 59:7).
bend--literally, "tread," or, "prepared." The allusion is to the mode of bending a bow by treading on it; here, and in Psa 58:7, transferred to arrows.
psa 64:4the perfect--one innocent of the charges made (Psa 18:23).
fear not-- (Psa 55:19), not regarding God.
psa 64:5A sentiment here more fully presented, by depicting their deliberate malice.
psa 64:6This is further evinced by their diligent efforts and deeply laid schemes.
psa 64:7The contrast is heightened by representing God as using weapons like theirs.
psa 64:8their . . . tongue to fall, &c.--that is, the consequences of their slanders, &c. (compare Psa 10:2; Psa 31:16).
all that see . . . away--Their partners in evil shall be terrified.
psa 64:9Men, generally, will acknowledge God's work, and the righteous, rejoicing in it, shall be encouraged to trust Him (Psa 58:10).