While I'm on the subject of diseased trees, I may as well write out the other analogy that has more profoundly affected me. I see weeds just as I see sin. I don't have to plant weeds in my flower beds or yard. They just come. I don't have to spend money and time planting them to have them come grow and begin to take over all things pretty. They come uninvited.
Do I ever have to teach my children to sin? NO. They just know how to do it. Because like weeds, it's just there. We are born with a sin nature.
I have to spend money to buy nice flowers and plants. I have to care for them so they don't die. I equate this to the efforts I need to put forth in my spiritual life. Also, to deal with weeds, we pull them at their roots to get rid of them. We spray weed killer on them. I don't have to make sure and water and give plenty of sunshine for a weed to grow....they just grow. I do however, have to water and give plenty of sunshine to the wanted flowers and plants.
Spending time saturated in the Word and spending time at the roots of sin will help me to have a maintained life, like the garden I so desire *grin*