Ps 94:11

“...We began with exulting joy: but this Psalm hath ended with great fear: "Unto whom I sware in My wrath, that they should not enter into My rest" (ver. 11). It is a great thing for God to speak: how much greater for Him to swear? Thou shouldest fear a man when he sweareth, lest he do somewhat on account of his oath against his will: how much more shouldest thou fear God, when He sweareth, seeing He can swear nought rashly? He chose the act of swearing for a confirmation. And by whom doth God swear? By Himself: for He hath no greater by whom to swear. By Himself He confirmeth His promises: by Himself He confirmeth His threats. Let no man say in his heart, His promise is true; His threat is false: as His promise is true, so is His threat sure. Thou oughtest to be equally assured of rest, of happiness, of eternity, of immortality, if thou hast executed His commandments; as of destruction, of the burning of eternal fire, of damnation with the devil, if thou hast despised His commandments. ...”