1 Corinthians 1:18 “For the message of the cross is foolishness to those who are perishing, but to us who are being saved it is the power of God.”

A fool is someone who is commonly known to lack good sense or judgement. Consider that the root word of foolishness it is the greek term ‘moria’, which literally means dull or lacking sharpness.
There is a certain disdain for foolishness in traditional christian thought. As a child, I was reminded on multiple occasions not to call someone a ‘fool’, lest I place myself under judgement. Jesus gave a scathing rebuke against this type of name calling and it is by this example much of christian doctrine centered.
Matthew 5:22 “But I say to you that whoever is angry with his brother without a cause shall be in danger of the judgment. And whoever says to his brother, ‘Raca!’ shall be in danger of the council. But whoever says, ‘You fool!’ shall be in danger of hell fire.”
I used to wonder why calling someone a ‘fool’ was such a big deal to Jesus, people act foolish all the time and the Bible goes into great length describing what a fool acts like, particularly in Proverbs. The term ‘Raca’ means empty or worthless, now it makes sense not to call someone worthless, I know that everyone has worth in God’s eyes, but people often leave no doubt that they are fools.
Paul called people foolish, especially the people from Galatia, for allowing the old law to become a part of their new found freedom in Christ:
Galatians 3:1 “O foolish Galatians! Who has bewitched you that you should not obey the truth, before whose eyes Jesus Christ was clearly portrayed among you as crucified?”
Galatians 3:3 “Are you so foolish? Having begun in the Spirit, are you now being made perfect by the flesh?”
The Lord, through Jeremiah called his own people foolish for their lack of faithfulness toward God and embracing idolatry:
Jeremiah 5:21 “‘Hear this now, O foolish people, Without understanding, Who have eyes and see not, And who have ears and hear not:”
Even Jesus Himself described people who were without the knowledge of Truth as foolish acting people:
Matthew 13:14 “And in them the prophecy of Isaiah is fulfilled, which says: ‘Hearing you will hear and shall not understand, And seeing you will see and not perceive;”

Matthew 23 is an entire chapter of Jesus bringing rebuke against the Pharisees, the religious elite of the day who looked holy from the outside but were hypocrites to the core. It seems from this chapter that it’s fine to call someone a hypocrite, Jesus makes mention of it several times and likewise fools in vs. 17 and 19 and also in Luke 11:40 and Luke 24:25.
So why the scathing rebuke against calling your brother…a fool?
Spiritual Error
When referring to someone as a fool, Paul and Jesus were referring to those who erred in the their spiritual understanding. The galatians had begun to allow old jewish practices to infiltrate their practice as christians under grace. The old letter of the law required people to strive toward perfection by observing the law, a perfection that was never obtained by anyone other than Jesus. The new order of grace allows the perfection of Christ to be the perfection of righteousness that we obtain by His sacrifice, to all who believe.
Clearly, you can be a christian and still act like a fool.
Listen to how the Bible describes fools:
“The fool hath said in his heart, There is no God. They are corrupt, they have done abominable works, there is none that doeth good… A brutish [stupid] man knoweth not; neither doth a fool understand this… Understand, ye brutish among the people: and ye fools, when will ye be wise… The fear of the LORD is the beginning of knowledge: but fools despise wisdom and instruction… O ye simple, understand wisdom: and, ye fools, be ye of an understanding heart… The wise in heart will receive commandments: but a prating fool shall fall… The lips of the righteous feed many: but fools die for want of wisdom… Fools make a mock at sin: but among the righteous there is favour… A wise man feareth, and departeth from evil: but the fool rageth, and is confident… A fool despiseth his father’s instruction: but he that regardeth reproof is prudent… The heart of him that hath understanding seeketh knowledge: but the mouth of fools feedeth on foolishness… He that trusteth in his own heart is a fool: but whoso walketh wisely, he shall be delivered… And every one that heareth these sayings of mine, and doeth them not, shall be likened unto a foolish man, which built his house upon the sand… For the wisdom of this world is foolishness with God. For it is written, He taketh the wise in their own craftiness” (Psalms 14:1, Psalms 92:6, Psalms 94:8, Proverbs 1:7, Proverbs 8:5, Proverbs 10:8, Proverbs 10:21, Proverbs 14:9, Proverbs 14:16, Proverbs 15:5, Proverbs 15:14, Proverbs 28:26, Matthew 7:26, and I Corinthians 3:19).

These fools are those that have not believed in the Lord, nor have they committed their lives toward Him.
Spiritual Deception
Deception comes from the enemy, it’s easy to blame others, particularly Satan for the deception of sin and the fall of mankind. “The devil made me do it”, is an often humorous but sobering excuse for those who don’t want to take ownership for their actions.
Deception is particularly effective in those who lack knowledge of truth.
John 17:17 “Sanctify them by Your truth. Your Word is truth.”
A brief survey of the Word of God gives an illustration of those who lack this knowledge:
“The way of a fool is right in his own eyes: but he that hearkeneth unto counsel is wise… Keep thy foot when thou goest to the house of God, and be more ready to hear, than to give the sacrifice of fools: for they consider not that they do evil” (Proverbs 12:15 and Ecclesiastes 5:1)
The difference between a Fool and acting like a Fool is in the heart.
Two Fools
Foolishness of Unbelief:
For those who have rejected the Savior, their hearts remain darkened by sin. There is an enlightenment that occurs upon receiving the Spirit of God in salvation.
Matthew 6:22 “The lamp of the body is the eye. If therefore your eye is good, your whole body will be full of light.”
The Holy Spirit is the One who calls sinners to repentance. It is He who likewise fills the heart of the one who responds in humility and a contrite spirit. Upon the change of heart comes the opportunity to receive wisdom.
Foolishness of disobedience:
Godly wisdom is not worldly wisdom, godly wisdom cannot be received by the world, it is imparted by God to His people.

1 Corinthians 2:7 “But we speak the wisdom of God in a mystery, the hidden wisdom which God ordained before the ages for our glory,”
Just because we have access to God’s wisdom as believers, doesn’t mean every believer draws from God’s source. The continual conflict of the flesh battles the Spirit of God who instructs and leads in a believers life. This sanctifying work of God’s Spirit leads those who embrace His instruction into maturity. Maturity is the mark of wisdom to those who walk obediently in Christ and allow Him to do His work in us.
When we brings the Word of God to a fellow believer that is walking in error, we are pronouncing their foolish behavior and giving them the necessary tools to walk in wisdom.
Hebrews 4:12 “For the word of God is living and powerful, and sharper than any two-edged sword, piercing even to the division of soul and spirit, and of joints and marrow, and is a discerner of the thoughts and intents of the heart.”
When we bring foolishness to light, we are bringing the light to the foolish.
Final Summary
When Jesus brought a scathing rebuke against His people for calling brothers fools (those who are in the faith), He was saying, don’t judge them as being unbelievers.
We cannot see the heart of mankind, the spiritual heart that is, therefore we cannot make a definitive statement regarding their salvation.
Matthew 7:1-5 “Judge not, that you be not judged. For with what judgment you judge, you will be judged; and with the measure you use, it will be measured back to you. And why do you look at the speck in your brother’s eye, but do not consider the plank in your own eye? Or how can you say to your brother, ‘Let me remove the speck from your eye’; and look, a plank is in your own eye? Hypocrite! First remove the plank from your own eye, and then you will see clearly to remove the speck from your brother’s eye.”
When I was a young man and was scolded for calling my brother or sister a fool, the instruction as to why I shouldn’t had been left out. The more I grew, the more I desired to have a right understanding of Truth so that I might walk according to the true purpose of God’s Word and not a mindless obedience that lacks understanding. I was mindless for a long time, it became oppressive in that it seemed I was following rules that made very little sense and therefore became a process of salvation by works.
I’ve learned that in the same way Jesus instructed us not to judge one another, was the same instruction He gave for labeling someone a fool. I finally began to understand why it didn’t make sense that I was called to judge fellow believers by their actions but not by their position in Christ. Believers may act foolish but that doesn’t negate their salvation. Unbelievers may try to act wise, this doesn’t indicate salvation either. We don’t need to judge the world, they already stand judged before God. Believers on the other hand stand by grace, God doesn’t condemn them and neither should we.
We have to make sure our own actions aren’t foolish before we address foolishness within the church. Once we get ourselves in line with God’s Word, we can share with others who may have gone astray, thus finally removing the plank from my brothers eye and helping him get back to victorious christian living.
For the true fool who has rejected the salvation that is found in Christ alone, we bring to them the gospel. The wisdom of the Word brings to the surface their error and hopefully leads them to Christ.