www.bible.com/111/mat.6.19.niv
We are not to put our trust in things of the world, because eventually everything of the world will be destroyed. Instead we are to put our trust in heavenly things, because these are the things that cannot be destroyed. Also, by putting our trust in heavenly things we show where our priorities lie. Our number one priority should always be Jesus and heavenly things not the things that the world values.