Must be (dei einai). Since moral conditions are so bad among you (cf. chapters 1 to 6). Cf. Mat 18:7.
Heresies (haireseis). The schisms naturally become factions or parties. Cf. strifes (erides) in 1Co 1:11. See Act 15:5 for haireseis, a choosing, taking sides, holding views of one party, heresy (our word). “Heresy is theoretical schism, schism practical heresy.” Cf. Tit 3:10; 2Pe 2:1. In Paul only here and Gal 5:20.
That (hina). God’s purpose in these factions makes the proved ones (hoi dokimoi) become manifest (phaneroi). “These haireseis are a magnet attracting unsound and unsettled minds” (Findlay). It has always been so. Instance so-called Christian Science, Russellism, New Thought, etc., today.