Charles H. Spurgeon on Psalms 90:12

So teach us to number our days, etc. Five things I note in these words: first, that death is the haven of every man; whether he sit on the throne, or keep in a cottage, at last he must knock at death's door, as all his fathers have done before him. Secondly, that man's time is set, and his bounds appointed, which he cannot pass, no more than the Egyptians could pass the sea; and therefore Moses saith, "Teach us to number our days", as though there were a number of our days. Thirdly, that our days are few, as though we were sent into this world but to see it; and therefore Moses, speaking of our life, speaks of days, not of years, nor of months, nor of weeks; but "Teach us to number our days", shewing that it is an easy thing even for a man to number his days, they be so few. Fourthly, the aptness of man to forget death rather than anything else; and therefore Moses prayeth the Lord to teach him to number his days, as though they were still slipping out of his mind. Lastly, that to remember how short a time we have to live, will make us apply our hearts to that which is good. —Henry Smith.