A while ago (I honestly can't remember when), I was having a conversation with my mom about I don't remember what. It must have had something to do with big decision making or spending time or something like that because she told me about doing random things for her boss at a job a long time ago. None of the other employees wanted to do things like drive across town to get something from the store, but she was okay with it.
When asked why, she said that her boss was paying her for her time so it was up to him how she spent it. It didn't really matter whether she was at a desk or in the car - she was being paid to give control of that time to someone else.
This wasn't just a random story though - she had a point. Our whole lives are the exact same way. They belong to God and we should be happy to spend them however He pleases.
Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, for you were bought with a price. So glorify God in your body. - 1 Corinthians 6:19-20
That thought is so incredible to me. God spent so much to save us and so our bodies, lives, and (on a smaller scale) time belong to Him.
Just the idea that every second of every day that I live belongs to God changes how I think and the choices I make. Think about it - what if you had to report to God what you did all day? Would you be on Facebook right now? Would you be done with schoolwork by now? I know I wouldn't waste time nearly as much.
But wasting time can happen in a lot of different ways. It might be spending too long on Facebook. But it also might be reading a trashy novel. It could be all sorts of things. Just because we seem to be doing something good (like reading) doesn't mean the actual thing we're doing is edifying.
We are called to use our lives to further the kingdom of God and every second that we waste is a second that we're not doing that.
That's not to say it's wrong to rest - just the opposite. Rest is a very good thing, but it must be done wisely. Too much is laziness, too little isn't good for you.
God has only given us so much time on this earth. We've got to be good stewards of it.