Ezekiel 15

“Son of man, how is the wood of the vine better than any other wood, the vine branch which is among the trees of the forest?  Is wood taken from it to make any object? Or can men make a peg from it to hang any vessel on?" vv.2-3

Read chapter 15
The figure of the vine is often use to describe the house of Israel.  "For the vineyard of the Lord of hosts is the house of Israel," Isaiah 5:7.  The whole purpose of the vine is to bear fruit, for if it doesn't it's useless.  The fruit of the vine is very valuable and useful.   Like many other trees that bear fruit, their wood can be useful even if fruit doesn't grow for the wood can be made and used in to many things.  Not so the wood of a vine, not even for one single peg in a wall could it be useful.  If it is barren the only use of it is to be fuel for fire.
There's the well know chapter fifteen in John of the true vine.  “I am the vine, you are the branches. He who abides in Me, and I in him, bears much fruit; for without Me you can do nothing."  Without God, Israel was nothing among the other nations.  Without God, we are worthless.  Only with Israel abided in their true God were they a great and prosperous  nation.  Only when we abide in Him can we bear much fruit and be useful and purposeful. 
What neglect do you have of God in your life has caused you to feel purposeless?  When have you felt fruitful and what was your relationship with God at that time like?