Original: In his Bull of 1302, Unam Sanctam, Boniface VIII proclaimed that it "is absolutely necessary for salvation that every human creature be subject to the Roman pontiff", pushing papal supremacy to its historical extreme.
Simplified: In his Bull of 1302, Unam Sanctam, Boniface VIII proclaimed that it "is absolutely necessary for salvation that every human creature be subject to the Roman pontiff", so he pushed papal supremacy to its historical extreme.