For God has already placed Jesus Christ as the one and only foundation, no other foundation can be laid.
1 Corinthians 3:11
When a carpenter begins to build a building like this, there is something very important that He needs. He needs wood. He needs windows. He needs nails. He Needs a hammer. He needs a lot of supplies, there is one thing that is more important then all these things and that is to build this building on a solid foundation. A carpenter cannot begin building like this on air. The air cannot support the weight of the wood. The wood will start to fall until it finds a solid foundation to support it. The carpenter cannot build a house on a foundation like this egg. A egg is hard on the outside but soft on the inside, when the right amount of pressure is applied to the wood the foundation will cave in. Every carpenter knows that if he is going to build a house that is worth anything, they have to build it on a solid foundation like this rock, if they build it on a solid foundation it will be able to with stand the pressure. Just like you. You have a solid foundation in Jesus. You have to build your life on the rock Jesus by studding His word, trusting him, and Doing what the word of God tells you to do.
Jesus was teaching the crowds about Gods Kingdom and how they should live there lives, He told them to build lives on a solid foundation, be wise and build your life on the Rock (Jesus) and the the sand.
Farther more you can't trust worldly foundations, be it jobs, relationships, or money, because these things don't last forever But Jesus is like this rock, He is solid and you can put your trust in Him. Jesus is the only one you can trust to build your life on!