save others: Some believers were so influenced by the false teachers that they were in immediate danger of being condemned.
to still others show mercy: This group likely includes the false teachers themselves or those who followed their teachings. Showing mercy might involve praying for them (see Matthew 5:44).
Believers must be very careful when showing mercy to false teachers and those who have adopted their sinful ways, as their sins can be tempting. See Zechariah 3:1–4; Revelation 3:4.