"Take care of yourself." Jehovah's Witnesses say this is wrong?

Did you know that JWs would lecture me for telling someone "Take care of yourself?" They would say that taking care of yourself is selfish, and if you get right down to it, evil. This scripture, however, seems to say otherwise. 

 "But you, dear friends, as you build yourselves up in your most holy faith and pray in the Holy Spirit, keep yourselves in the love of God, expecting the mercy of our Lord Jesus Christ for eternal life." Jude 1:20