In the world there are different meanings in every country as well as in every religion. But for now the Chinese people give a beautiful clarification to this reason. Which is the thumb represents your parents. The index finger represents your siblings. The middle finger represents yourself. The ring finger represents your life partner and the little finger/pinky represents your children.
For this matter hold your hands together like the picture. Join your middle fingers back to back and the remaining fingers tip to tip. Now, try to separate your thumbs. They will separate because your parents are not intended to live with you forever. Rejoin your thumbs and separate your index fingers. They will separate because your siblings will have their own families and lead their own lives. This is reason which is not worn on these fingers.
And also when rejoin your index fingers and separate your little fingers/ pinkies. They will separate because your children will grow up, get married, and settle down.
At the last rejoin your little fingers/pinkies and try to separate your ring finger. They will not be able to separate because your life partner is meant to be with you all the way through your whole life, through broad and slender. This is all about live and get a meaning for your life.