"What is this magical stuff?" he thinks. Kids are awesome like that. They are amazed by simplest things.
So after playing for awhile the child wants to take some of this sand for keeps. Who can blame him? It's great stuff!
But it just keeps slipping through his fingers. He can’t figure out to hold on to this sand and make it his own for good.
How cruel would it be for the Dad to say to the three year old son. “Son, just keep trying. Keep grasping. Keep reaching. One of these times you’ll get it. I know you are getting increasingly frustrated by your lack of ability to hold on to it, but just keep at it. Keep striving.” It’s cruel because it doesn’t work! That kid will never be able to grasp the sand.
No, what is much more loving is for the Father to say, “Son, just enjoy it right now. You can’t take it with you. Just be content with it right here at the beach. If you try and try to hold on to it you’ll miss the reason we are at the beach in the first place. It will ruin your experience here and you weren't built to keep the sand."
 But godliness with contentment is great gain,  for we brought nothing into the world, and we cannot take anything out of the world.  But if we have food and clothing, with these we will be content.  But those who desire to be rich fall into temptation, into a snare, into many senseless and harmful desires that plunge people into ruin and destruction.  For the love of money is a root of all kinds of evils. It is through this craving that some have wandered away from the faith and pierced themselves with many pangs.
 As for the rich in this present age, charge them not to be haughty, nor to set their hopes on the uncertainty of riches, but on God, who richly provides us with everything to enjoy.  They are to do good, to be rich in good works, to be generous and ready to share,  thus storing up treasure for themselves as a good foundation for the future, so that they may take hold of that which is truly life. (1 Timothy 6:17-19 ESV)