Generally whenever the phrase "but" appears, it basically means that what was said before is as good as nonsense.
Seeing their anxious expressions, Lord Taishang smiled and said, "However, we the Three Pure Ones will not intervene in the struggles between the living beings of later generations and the Ancient Gods. If you wish to protect these living beings, you must take action yourselves."
"Why not intervene?"
Sun Wukong glared at Lord Taishang.
Lord Taishang smiled faintly and said, "From ancient times until now, there have been too many Ancient Gods dissatisfied with us three. Should we intervene, it would surely incite a great war among the Ancient Gods, and then it would not be about protecting the living beings of the Three Realms but potentially crippling the entire Three Realms."
So that was it, Sun Wukong and the others were relieved.
Lord Taishang and the others were not worried about their own safety; they had been aloof from the beginning of time until now.