We say that to 'give up all evil and to develop the good' is the heart of the Buddha's teaching. If we only make merit but have not stopped doing bad things, then we will never have a day of completion. It is like an overturned bowl which is left outside in the rain. Even if the water is falling right on it, it only touches the outside and not the inside. In this way the bowl will never get full.
Ajahn ChahRegarding this Dhamma, it is not something that we can simply talk about or take another's word for it. We need to develop meditation so that the understanding arises clearly within oneself. It is not the case that merely by listening to another's explanation our defilements will disappear. When we gain some understanding we need to chew on it again so that we see it for ourselves with certainty: paccattam.
Ajahn ChahThe Dhamma has to be found by looking into your own heart and seeing that which is true and that which is not, that which is balanced and that which is not balanced.
Ajahn Chah