Jeremiah 17:7-8
"Blessed is the man who trusts in the Lord whose confidence indeed is in the Lord. He will be like a tree planted by water; it sends its roots out toward a stream, it doesn't fear when heat comes, and its foliage remains green.  It will not worry in a year of drought or cease producing fruit."

Faith saves us so that we may place trust in the Lord.  When that happens the person may then be nourished and grow to be a great tree.  No matter the size it is green and healthy; heat cannot scorch it or sap it of its strength.  Drought will not kill its leaves or fruit, for it can withstand any conditions.  This tree knows where the stream is, its source of life, and it wisely grows its roots out toward the stream for constant food.  What need is there to worry for this stream never dries up or ceases to flow.  Times of drought and heat may come and consume those with insufficient root growth, but not the tree who has been planted by water.  This tree is the man who completely trusts in the Lord, abides in Him, and obeys Him.