This analogy also works for the sin in our lives. When we do things that we know we shouldn't do, we are effectively throwing trash into our own lives. When we hold on to sin in our lives, instead of asking for forgiveness from God, it begins to collect in the streets of our brains and the rivers of our hearts.
If we let those things build up in our lives, it can be very hard to get them out. Let me give an example of what I mean. As I was cleaning along the river bank, I came to where a house used to stand, but was washed away. Even though the house was gone, there was trash tangled in the old foundation that had obviously been there since November...like clothes and blankets that were wedged under heavy rocks and shredded bags tangles around exposed pipes. I tried to pull at it to trow it out, but it was so tangled and rotten, wedged in and stuck with mud and nastiness that it wouldn't budge. I tugged and tugged, but it would have taken two guys to pull the rocks off it and maybe a knife to cut it free of the branches, metal bars, and debris that it was snared in. Since it had been there since November, it was ODORIFEROUS!! This is just like trash that has been left in our lives, from other people throwing it at us and from our own selves letting it collect from un-confessed sin. If left long enough, it too will begin to rot. This is what the Christian dictionary calls "bitterness". We can probably all think of a person or two who has let the trash of this life collect to the rotten point.
Of course, as a good Calvin College student and steward of this planet, I also have to give a plug for saving our planet. Reduce, reuse, recycle (sayings from my generation). It is important to not only pick up the spiritual trash we collect, but natural, physical trash, too. Let's leave a clean planet for our children's children's children's children's children's children's children.