In this passage, "the world" is a metonym for the people who oppose God. (See: [[rc://en/ta/man/translate/figs-metonymy]])
# keep them from the evil one
This refers to Satan. AT: "protect them from Satan, the evil one" (See: [[rc://en/ta/man/translate/figs-explicit]])
# Set them apart by the truth
The purpose for setting them apart can be stated clearly. The phrase "by the truth" here represents by teaching the truth. AT: "Make them your own people by teaching them the truth" (See: [[rc://en/ta/man/translate/figs-explicit]])