Solomon employs interesting metaphors in this passage. The "keepers of the house" in verse 3 are a person's arms. We work with our hands and arms, and they keep the house. In time, they begin to tremble—he is referring to the progression of old age.
"The strong men bow down"—the legs, the knees, begin to get weary, to bow from the weight of the body on top of them.
"When the grinders cease"—a person's teeth—"because they are few"—they are falling out. "And those that look through the windows"—are the eyes, which are growing dim.
"When the doors are shut"—when the older person tends to stay inside because he feels more comfortable and safe being closed up in the house. He does not worry about having a heart attack out on the street. Many older people become reclusive as they age.
"And the sound of grinding is low"—he refers to work cycles, using the grinding of grain as a representation of work in general. Apparently, in those days, the whole community ground grain together. The town would have one mill, and everyone would come and have a lot of fun, laughing and enjoying the friendship, companionship, and fellowship with others at the mill. But as a person gets old, he does not have the strength to go to the mill and enjoy the pleasures of that work.
"When the almond tree blossoms"—it turns white. Solomon is talking about the hair turning gray and then white.
"And the grasshopper is a burden" is an interesting picture. Everybody knows how light a grasshopper is, but even the lightest thing becomes a burden to an older person because he is losing his strength.
"For man goes to his eternal home"—the grave—"and the mourners go about the streets." Death is seen as the climax of a process that began with birth and the strength of youth.
John W. Ritenbaugh
Ecclesiastes and the Feast of Tabernacles (Part 2)