1 Corinthians 11:19 (ESV)

19 for there must be factions among you in order that those who are genuine among you may be recognized.

Paul has realistic expectations of the church community. He knows that there are some church members who do not have true faith. Due to this fact, there must be factions.

Whereas the word divisions (schismata) in verse 1 Corinthians 11:18 has a clearly negative connotation, factions (haireseis) is a neutral word that indicates choice or voluntary separation. Any religious group can be described as a faction (see Acts 15:5, for example), since its members willingly set themselves apart by their particular beliefs and customs.

Factions, although they emerge from human sinfulness, are decreed by God for the good of the church. There must be factions, in order to test who is genuine (literally, approved after testing).

When Paul speaks of factions, he may have in mind the true believers in the Corinthian church who are distancing themselves from the false (or disobedient) believers. This understanding fits well with the second part of the verse. It is also in keeping with a passage in Paul’s second letter to the Corinthians, where he warns believers against spiritual partnership with unbelievers (2 Corinthians 6:14 – 7:1).

Alternatively, the factions might be those groups in the Corinthian church who are causing division through their unbiblical beliefs and actions (cf. Galatians 5:20).