Psalm 90 Part 3 v12-17

Moses lived 120 years according to Deuteronomy31:2 and 34:7. He did not say 70yrs(v10) was either a promise or a limit but as a poetic estimate of a lifespan. The emphasis is on the futility of life; even if one should live past the norm of 70 and live eighty years, the end of it all is ‘only labour and sorrow.’ Moses here is overwhelmed with the terrible results of divine displeasure; evidenced by the wilderness wanderings and rebellion of his people.

When Moses considered the shortness and miseries of life and the frail nature of humanity and the righteous judgment of God, it made him ask God for the wisdom to understand the shortness of life. It seems people can number everything: populations, cattle, bank accounts, properties, birthdays, and yet somehow seem to persuade themselves that their days are innumerable when in actuality they are destined for dust. 
Young people especially often think their days have no number and give little thought to what lies beyond this life. If we were ‘wise’ we would consider our own frailty and the shortness and uncertainty of life. We would then live for eternity by acquainting ourselves with God and be at peace.

The final section (13-17) is Moses appeal (prayer) to the infinite God, appealing to his lovingkindness (chesed) – His loyal covenant love. Isaac Watts’s famous hymn was inspired by this section “Our hope in ages past will be our hope in years to come.” 
Moses carefully considered the judgment of God, and yet his prayerful response to that consideration was a plea to God for His presence, for His compassion, and for His ‘lovingkindness’ (NKJV: Mercy.)

2Cor4:17 does the same as v15, by balancing our sorrows with the promise of ‘an eternal weight of glory beyond all comparison.’ The time of our pilgrimage upon earth is a struggle and a time of sorrow; we grieve for our departed friends and our surviving friends must soon grieve for us; these are days wherein we are afflicted that we might lift our sights to the immensity of eternity.  3500-year-old wisdom!  ‘Let the favour of God be upon you!’v17.