That sin is thus practical [engages in actions, practice] and full of action will appear if you consider two things:
1. The fruitfulness and the plentiful increase that it does bring forth.
2. And the power and vivacity that there in sin, both which will set out, that the enemy against whom we do contend against is an active and stirring enemy.
Sin Spreads With Great Speed
Even as when you cast a stone into a pond that begets a circle, and that begets a greater, and so they multiply until be many, and that on a sudden. So is it case of sin, one sin begets another speedily, and the reason is, because it is the nature of the worst kind of fruit to spring fastest.
No one Needs to Cultivate Weeds or Sinful Desire
You need not plow for weeds, nor sow cockle nor hemlock in the furrows of your field, they will grown of themselves. So it is with the ill weeds of sin, they come up of their own accord; nay, though we labor to weed out these corruptions, yet will they sprout and grow again. If you ask me why that grace grows so slowly and sin with such speed, I answer as the Egyptian midwives did unto Pharaoh when he asked them why they slew not the male children, they answered, because they are not as the Egyptian women, but lively and are speedily delivered (Exod. 1.19).
So it is in this case, grace at the first is weak, compared to a grain of mustard seed, and falls into a barren soil, our corrupt hearts, and there it is that it comes up so slowly; but sin, that is strong and is in a soil that it likes, and therefore comes up with more celerity.
 By “lust”, Wolfal means strong desires –whether sexual or otherwise. Here “lust” refers to the profound desires to sin caused by indwelling sin. The wording comes from Galatians 5:17, where the word often translated as “desire” was previously translated by the English word “lust”. Ed.
 Again, this is much in common with other Puritan teaching. Thomas Brooks in his work Precious Remedies Against Satan’s Devices writes that, “Sin is a plague, yea, the greatest and most infectious plague in the world …. The sin that is in one man’s heart is able to infect a whole world, it is of such a spreading and infectious nature.”