The word "heresies" refers to opinions that are contrary to the teaching of Christ and the apostles. These heresies destroy the faith of those who believe them.
The word "master" here refers to a person who owns slaves. Peter speaks of Jesus as the owner of people whom he has bought, the price being his death. (See: [[rc://en/ta/man/jit/figs-metaphor]] and [[rc://en/ta/man/jit/figs-explicit]])