Caution and fear are the legacy of knowledge and its measure; knowledge is the ray of gnosis and the heart of belief. Whoever is denied caution is not a man of knowledge, even if he can split hairs in dealing with obscure items of knowledge. Allah said,
Only those of His servants who are possessed of knowledge fear Allah. (35:28)
Men of knowledge are ruined by eight things: greed and miserliness, showing off and partisanship, love of praise, delving into things whose reality they cannot reach, affectation by taking excessive pains to beautify their speech with superfluous expressions, lack of modesty before Allah, boastfulness, and not acting upon what they know.
‘Isa [a] said, 'The most wretched of all people is he who is known for his knowledge, not for his actions.'
The Holy Prophet said, 'Do not sit with every presumptuous caller who summons you from certainty to doubt, from sincerity to showing off, from humility to pride, from good counsel to enmity, and from abstinence to desire. Draw near to the person with knowledge, who summons you from pride to humility, from showing off to sincerity, from doubt to certainty, from desire to abstinence, from enmity to good counsel.' None are fit to preach to creation except that person who has gone beyond these evils by his truthfulness. He sees the faults of speech and knows what is sound from what is unsound, the defectiveness of thoughts, and the temptations of the self and his fancies.
'Ali said, 'Be like the kind, compassionate doctor who places the remedy where it will be of benefit.' They asked ‘Isa [a], 'With whom shall we sit, O Spirit of Allah?' 'With one the sight of whom reminds you of Allah,' he replied, 'and whose speech increases you in knowledge, and whose actions make you desire the next world.'