Only Castles Built on the Rock Will Remain

I heard the Spirit of the Living God say, 
Castles of sand are being built alongside castles of stone. To the outside eye, they don’t appear to be very different. The castles of sand seem to be built and established much more quickly than the castles of stone. A greater number of the castles of sand are being built, because the castles of stone require more tedious work. But when the waves come, the people will see what remains.