Humans only live a short time because God judges the sin in their lives (cf. Psalm 90:14-1544). God knows even our secret sins. They do not escape Him, and He judges us with physical death for our sins. [source][source][source]
Assuming Moses did write this Psalm , it is interesting that he said the normal human life span was70 years. He lived to be120 , Aaron was123when he died, and Joshua died at110. Their long lives testify to God"s faithfulness in providing long lives to the godly, as He promised under the Mosaic Covenant. [source][source][source]
Since our lives are comparatively short we should number our days ( Psalm 90:12). Moses meant we should realize how few they are and use our time wisely (cf. Ecclesiastes 12:1-7). Notice how often Moses mentioned "our days" or the equivalent in this psalm ( Psalm 90:4-6; Psalm 90:9-10; Psalm 90:12; 1713383774_1). [source][source][source]
"The pivotal point of the text, I suggest, is the goal of a "heart of wisdom" ( Psalm 90:12)." [1][source]
A heart of wisdom refers to discernment of Yahweh"s purposes. [source][source][source]