In FAQ of Opalescence, I see an example of interaction between Opalescence and Humility:

So if Opalescence, Humility, and Worship are on the battlefield and Opalescence entered the battlefield before Humility, the following is true: Layer 4: Humility and Worship each become creatures that are still enchantments. (Opalescence). Layer 6: Humility and Worship each lose their abilities. (Humility) Layer 7b: Humility becomes 4/4 and Worship becomes 4/4. (Opalescence). Humility becomes 1/1 and Worship becomes 1/1 (Humility).

But I have a question. If Humility cause itself loses all abilities at layer 6, why it can still change the P/T in layer7b?

Once an effect starts applying in one layer, it will also apply in all layers above that one, even if the effect disappears somewhere in those layers. Since Humility applies in layer 6, it also applies in layer 7b. If another effect was applying only in layers 7b and 7d and disappear in layer 6 due to Humility, then it wouldn't apply at all (it disappeared before it started applying).

Daniel Kitachewsky
L4, Paris, France
Rules NetRep