"against your enemies": (Keep it in mind that you are going out) against your enemies, (and act accordingly).
"then you shall guard yourself against every evil thing": I might think that this refers to (the need for circumspection vis-à-vis) cleanliness, uncleanliness, and tithes; it is, therefore, written (Ibid. 15) "and He shall not see in you a thing of nakedness" (ervah). This tells me only of "ervah." Whence is included (in the need for circumspection) idolatry, bloodshed, and blasphemy? From "then you shall guard yourself against every evil thing." Just as "ervah" is distinct in that it is something for which the Canaanites were exiled and because of which the Shechinah is removed, so, all such things (are included).