"Because of laziness the building decays, And through idleness of hands the house leaks." (Ecclesiastes 10:18)
IF OUR GOAL IS GODLY CHARACTER, THAT GOAL WILL NOT BE REACHED BY ACCIDENT OR BY INACTIVITY. The fact that salvation is by grace means many things, but it doesn't mean that the lazy will be saved. To Timothy, Paul wrote, "Be diligent to present yourself approved to God" (2 Timothy 2:15). It's only those who love God enough to seek Him energetically who one day will receive the benefit of having sought Him. The lazy are going to be lost!
Physically speaking, a building "decays" when its owners don't maintain it, and "through idleness of hands the house leaks." Do-nothingism never leads to anything but a dilapidated state of affairs. Left to themselves, physical things deteriorate.
In the spiritual realm, the consequences of laziness are even more serious.
A house leaking because its roof has not been maintained is nothing compared to a human soul that has been neglected. When effort is not expended to grow toward God, the corruption and decay that result in the human heart are shocking.
So the disciplines that lead to godliness take work. This work does not earn or merit our salvation, it's true. But it's also true that without work we will certainly forfeit our salvation (Hebrews 6:11,12). Heaven is for the interested, the energetic, and the industrious. And we need not say that we're industrious toward God if our actual daily habits don't show that.
Whether it's serving others in the name of Christ or the more private activities of Bible study, prayer, and meditation, we can't claim to be working hard on the "house" of our godliness if, at the end of the day, our timelog doesn't show that we've spent much time doing these things. Under normal circumstances, a lack of activity indicates a degree of laziness. And laziness leads to leaky houses, always.
"I discover an arrant laziness in my soul. For when I am to read a chapter in the Bible, before I begin I look where it ends. And if it ends not on the same side, I cannot keep my hands from turning over the leaf, to measure the length on the other side; if it swells to many verses, I begin to grudge.
Surely my heart is not rightly affected. Were I truly hungry after heavenly food, I would not complain of meat. Scourge, Lord, this laziness of my soul; make the reading of your Word, not a penance, but a pleasure to me; so I may esteem that chapter in your Word the best which is the longest" (Sir Thomas Fuller).