Here the word "heart" represents the mind and thoughts. The abstract nouns "meditation" and "understanding" can be translated as verbs. AT: "the thoughts upon which I meditate will help you to understand" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-abstractnouns]])
The writer speaks of listening carefully to something as if it were bending one's ear towards the person who is speaking. AT: "listen carefully" (See: [[rc://en/ta/man/translate/figs-metaphor]])
The writer asks this question to emphasize that he has no reason to fear when bad things happen. AT: "I have no reason to fear ... heels." (See: [[rc://en/ta/man/translate/figs-rquestion]])
# the days of evil
"when evil things happen." Here the word "days" refers to general periods of time.
# when iniquity surrounds me at my heels
Possible meanings are 1) the writer speaks of the evil desires of his enemies as if it were a predator ready to overtake him. AT: "when the iniquity of sinful men is ready to overcome me" or 2) the writer's enemies surround him as they commit their iniquity. AT: "when my enemies surround me" (See: [[rc://en/ta/man/translate/figs-metaphor]])