3 Or backward turn its course from heaven's height;
backward > (See 2 Kings 20.10)
4 Sometimes great hosts of men she could dismay;
hosts > armies (see Judg. 7.21) dismay > defeat
5 Dry-shod to pass, she parts the floods in tway,
parts > (See Exod. 14.21 ff.) tway > two
6 And eke huge mountains from their native seat
eke > moreover mountains > (See Matt. 21.21) native seat > natural throne (i.e. foundations)
7 She would command themselves to bear away, 8 And throw in raging sea with roaring threat.
threat > pressure, thrust, hence: force (Latin trudere, to press, thrust, urge); also: threat, peril