"Your basic purpose of cultivating samadhi is to transcend the wearisome defilements. But if you do not renounce your thoughts of killing, you will not be able to get out of the dust." The Buddha means, after lust, if you already conquered the lustful mind, but still... You already cut off defilement in one department, but if your mind still doesn't cut off the thoughts of killing, or violence, or harm to others, then you don't get out of the samsara dust. Samsara, this world's dust; meaning thrown again and again in the dust and carrying this dusty body, which is made of dust. Buddha said it like that, meaning you can never get out of the physical existence.