Vishnu said Doing your good is my imperative duty; therefore am I speaking of the means by which he shall cease to exist.
विष्णुरुवाच अवश्यं करणीयं मे भवतां हितमुत्तमम्। तस्मादुपायं वक्ष्यामि यथाऽसौ न भविष्यति॥