Must be (δε εινα). Since moral conditions are so bad among you (cf. chapters 1 to 6). Cf. Matthew 18:7.

Heresies (αιρεσεις). The schisms naturally become factions or parties . Cf. strifes (εριδες) in 1. Corinthians 1:11. See on Acts 15:5 for αιρεσεις, a choosing, taking sides, holding views of one party, heresy (our word). "Heresy is theoretical schism, schism practical heresy." Cf. Titus 3:10; 2. Peter 2:1. In Paul only here and Galatians 5:20.

That (ινα). God's purpose in these factions makes the proved ones (ο δοκιμο) become manifest (φανερο). "These αιρεσεις are a magnet attracting unsound and unsettled minds" (Findlay). It has always been so. Instance so-called Christian Science, Russellism, New Thought, etc., today.