In Jewish culture the right hand was considered cleaner, more powerful, more concise, and held a place of honor. Jesus went to sit at the right hand of God (Mark 16:19), the priest and patriarchs blessed with their right hand, lepers were purified by applying blood to their right appendages, and Jews always fed themselves with the right hand. On the other hand, literally, the left was used for filthy, disgusting, and disgraceful acts. For example, like cleaning oneself after using the bathroom. It was considered weaker, clumsier, and dirtier. Also in Jewish culture the North side of the Earth was considered it’s Right side and was a place of brightness, while the south was considered it’s left side and was a place of darkness. So with all that in mind lets read that verse again:
“A wise man’s heart is at his right hand; but a fool’s heart at his left.” – Ecclesiastes 10:2
When your heart is set on the brighter things (spiritually speaking), clean things, honorable things, and being fed spiritually, wisdom will come. However when your heart is set on darkness, filth, unclean thoughts, and spiritually dishonorable acts, foolishness is the inevitable outcome. My dad always said it best, simple and plain, “sin makes you stupid”.
“The fool hath said in his heart, There is no God. They are corrupt, they have done abominable works, there is none if them that doeth good.” – Psalms 14:1
“A good man out of the good treasure of his heart bringeth forth that which is good; and an evil man out of the evil treasure of his heart bringeth forth that which is evil: for of the abundance of the heart his mouth speaketh.” – Luke 6:45
“The fear of the Lord is the beginning of knowledge: but fools despise wisdom and instruction.” – Proverbs 1:7