Psalm 90:1-12 - This Psalm is the appointed one for this Sunday. Verse 17 is the key verse, “Let the favor of the Lord our God be upon us.” The Psalmist asks, As You Lord only have been our security in the world so also make our labors to be effective and enduring – though we are so transient.
Not all of the psalms were written by David. Psalm 90 is one of those exceptions. There is a notation which reads, “A Psalm/Prayer of Moses the man of God.” In this psalm Moses directs us to consider God’s eternity and man’s life as transitory. In the midst of this psalm lies verse 10, “As for the days of our life, they contain seventy years, or if due to strength eighty years. Yet their pride is but labor and sorrow. For soon it is gone and we fly away.’ (NASV) Or, as the King James Version renders this verse, “The days of our years are threescore and ten; and if by reason of strength they be fourscore, yet is their strength labour and sorrow; for it is soon cut off, and we fly away."
Moses lived roughly 2,000 years before Christ. Thus, this psalm is nearly 4,000 years old. What Moses declares and what we know by experience; for the past four thousand years the average human life span is between seventy and eighty years. Compared to eternity our life is brief and short-lived. Thus Moses asks the LORD, ”So teach us to number our days, that we may present to Thee a heart of wisdom.” Our time on earth weighed against eternity, there is no comparison. Thus we ask the LORD to apply our hearts to wisdom so we may be about the business of gossiping the gospel serving our neighbor in love.
We are not given to know how long our life shall be. Some are longer; others short. Thus we ask the LORD to direct our path and order our day as we prepared to spend eternity with Christ in glory.
Collect for Psalm 90: Eternal Father, of our mortal race, in Jesus Christ your grace has come upon us. For his sake, prosper the work of our hands until he returns to gladden our hearts forever. 
 Collect for Psalm 90, For All the Saints, A Prayer Book for and By the Church Vol.II © 1995 The American Lutheran Publicity Bureau, Delhi, NY