Does it matter whether a Mayfly lives for 30 minutes or 45?

Why should we be advised to number our days aright? Moses wrote this psalm a whopping 3500 years ago and it still has relevance,God's word,like God Himself is eternally significant ,isn't it...

Babies suddenly dying,young men getting fatally shot, Ebola spreading fast,Christians being persecuted in Iraq,hopelessness feeding nihilistic thoughts like wind blowing on a forest fire! It's important to know, whether there is a purpose to life or if everything is a mere puff of smoke? Some of us are so sure that there is purpose and yet,despite having the gift of that conviction ,are too lazy to act upon it.. so then even this important question loses significance,if we continue in our slumber.

Daniel 12:3 "Those who manifest wisdom will shine like the brightness of the expanse of heaven, and those who turn many to righteousness will shine like the stars for ever and ever."

"He is no fool who gives what he cannot keep to gain that which he cannot lose." Jim Elliot

Anyway,here's hoping the wise words of Ben from the sermon Number Our Days, wake me up:

Moses contrasts the eternity of God with the brief span of our ephemeral lives.
The playwright Samuel Beckett vividly put it like this: "They give birth astride of a grave, the light gleams an instant, then it's night once more" .
In the grand scheme of things our lives are brief and insignificant. No more important than grass that shoots up in the cool morning, but by the end of a sun-scorched Middle Eastern day is parched and withered.
It's humiliating to realise this, but until we do we will never gain a heart of wisdom: we will never be able to live our short lives well.
We think our lives are so important and so significant that we have become desperate to prolong them in any way we can. Two headlines from the BBC news website just last week:
On Wednesday, Tests raise life extension hopes"A drug discovered in the soil of a South Pacific island may help to fight the ageing process, research suggests." And on Thursday, Proof mounts on restricted diet"Cutting calories may delay the ageing process and reduce the risk of disease." Because of our self-importance, we are desperate to live for longer and longer.
And, of course, lots of stuff has been written about Michael Jackson that may or may not be true, but in 1986 he reportedly said that "I believe if I treat my body properly I'll live to be at least 150" . What are we to make of that?
How we need humbling! Against the background of eternity, what does it matter whether we live to seventy or eighty, or even 150? About as much as it matters whether a mayfly lives for 30 minutes or 45.
Where does this feeling of self-importance come from? Every day that passes we are reminded of the fragility of life. Soldiers are killed in Afghanistan. Someone dies from swine flu. A teenager is stabbed. A car crashes.
When Hannah, my first daughter, was a baby, her life seemed so tiny and fragile. I used to go into her room at night and just watch her sleeping, and I'd silently urge her just to keep breathing: just keep breathing for the next seventy or eighty years and you'll be OK.
Our lives are so fragile, but how quickly we forget that. How quickly we gain foolish self-importance, actually thinking that we matter as far as the world is concerned.
The wisdom we should learn from these first 6 verses, is that only the things we do that connect with eternity have any significance. Unless we can somehow plug ourselves into the eternal reality, then our lives will never have any meaning. We will never learn to live well.
Like that plankton I mentioned earlier:(Just as the vast ocean is the context for the life of a plankton, a microscopic sea creature, so the eternity of God is the context of each of our lives. In him we live and move and have our being.r)
 removed from it's context, the sea, it has a brief and pointless existence. Our lives, taken out of their eternal context, are equally brief and pointless.
Be awed by God's eternity. Be humbled by life's brevity.
...
  the reason that our lives have lost contact with the eternal is because they are lived under God's wrath.How do these things help us? How should our hearts react to these truths? Well, if we truly understand these things, then we will do what Moses does and cry out for reconciliation. We need to cry out for God's favour, verse 13 to 17.
Since our great problem is that God's wrath at our rebellion disconnects us from the eternal, the only solution is for God to reconnect us with him.
This is Moses' prayer. He prays that God would relent and have compassion. He prays for God's love to provide an answer to his wrath. He prays for gladness in place of sorrow. He prays for their works to be established rather than swept away. Moses rightly longs for significance in life, and he knows that it can come only through restored relationship with God.
But God's anger against us as rebellious people who have turned our backs on him needs to be dealt with. 
...
 Or perhaps you are fearful of your death. This is a right reaction to living under the wrath of God. Verse 7, We are consumed by your anger and terrified by your indignationref. You are right to be terrified if you are not in good standing with God.But we no longer have to live under God's wrath! If we so choose, we can live under his favour. If we make Jesus our Lord, and trust our lives to him, then death loses its sting; it simply becomes the doorway to life.
If you have already taken that step: if you are already confident in your relationship with God because you have put your trust in the death of his Son, then numbering your days will have a different effect. It will teach you to live your lives wisely. It will teach you to spend yourself on things that matter in eternity. Not to devote yourself to jobs and television and sport and entertainment and triviality, but to find all our gladness and satisfaction in God himself.