You may learn by us not to go beyond WHAT is written

[TonyChanYT]

1 Corinthians 3:

4For when one says, “I follow Paul,” and another, “I follow Apollos,” are you not being merely human?
5What then is Apollos? What is Paul? Servants through whom you believed, as the Lord assigned to each. 6 I planted, Apollos watered, but God gave the growth. 7So neither he who plants nor he who waters is anything, but only God who gives the growth. 8He who plants and he who waters are one, and each will receive his wages according to his labor. 9For we are God’s fellow workers. You are God’s field, God’s building.

21 So let no one boast in men. For all things are yours, 22whether Paul or Apollos or Cephas or the world or life or death or the present or the future—all are yours, 23and you are Christ’s, and Christ is God’s.

This continues to 1 Corinthians 4:

6 I have applied all these things to myself and Apollos for your benefit, brothers, that you may learn by us not to go beyond what is written, that none of you may be puffed up in favor of one against another.

What refers to?

It refers to "all these things".

"all these things" refers to?

1. Don't boast in Paul, Apollos, or Cephas.
2. Don't boast in men.
3. You belong to Christ.
4. You don't belong to any faction or men.
5. You are God's building.

Paul issues the warning not to go beyond what is written to specifically combat factionalism within the nascent church.