In plain words
That is why this body was formed for the very purpose of doing good deeds, good conduct and good thoughts. This body was ordained for the practice of Dharma. 'Śarīramādyaṃ khalu dharmasādhakam.' If this body was formed for the very practice of Dharma, then we must keep this body in the right condition.
This body is like a tool. Only when this tool is in the right condition can we do the work we have resolved on in the right way. We have a tool, a pen. If we want to use it, we must put it in the right condition. The nib must be right. There must be ink in it. Only when it is kept in the right way is it of use for writing. A knife is a tool. But only when that knife too is properly sharp can we put it to good use. So it is only when each tool is right in its own condition that we can do each of those jobs properly. This body too is just a tool. For this doing of karma, you must keep this body in the right condition. With a knife we can push through fruit, through vegetables, through any other tangled knots; we can cut them. If instead we try to cut iron with a knife, this knife too will lose its edge. In just the same way, you must use this body with discriminating knowledge, knowing in which tasks it should be put to good use. Here, whatever task we set out to do, we must put the question to ourselves there. I am Brahman, whose nature is the Ātma. I am dwelling in this body. 'I, whose nature is the Ātma, I, whose nature is Brahman, may I do these karmas with this body, or must I not?' So you must inquire. You must also inquire whether this karma is fit to be done or unfit to be done. Only then will you be one who has put this body to good use. You must not use this body as you please just because, after all, you have a body. That itself would amount to using it in actions against Dharma. This body was formed for the practice of Dharma; this body was ordained to be the temple of God.