Kumayl bin Ziyad Nakha'i says that once Imam Ali put his hand in his hand and took him to the grave-yard. When he passed through it and left the city behind, he heaved a sigh and said:
"Kumayl, these hearts are containers of the secrets of knowledge and wisdom and the best container is the one which can hold the most and what it holds, it can preserve and protect in the best way. Therefore, remember carefully what I am telling you.
Remember that there are three kinds of people:
One kind is of those learned people who are highly versed in the ethics of truth and philosophy of religion (knowers, masters),
Second is the kind of those who are acquiring the above knowledge (seekers),
and the third is that class of people who are uneducated (ignorant). They follow every pretender and accept every slogan, they have neither acquired any knowledge nor have they secured any support of firm and rational convictions.
Remember, Kumayl, knowledge is better than wealth because knowledge protects you while you have to guard wealth. Wealth decreases if you keep on spending it but the more you make use of knowledge the more it increases. What you get through wealth disappears as soon as wealth disappears but what you achieve through knowledge will remain even after you.
Kumayl ! Knowledge is power and it can command obedience. A man of knowledge during his lifetime can make people obey and follow him and he is praised and venerated after his death. Remember that knowledge is a ruler and wealth is its subject.
Kumayl ! Those who amass wealth, though alive, are dead to realities of life, and those who achieve know- ledge, will remain alive through their knowledge and wisdom even after their death, though their faces may disappear from the community of living beings, yet their ideas, the knowledge which they had left behind and their memory, will remain in the minds of people".
Kumayl says that after this brief dissertation, Imam Ali pointed towards his chest and said, "Look Kumayl! Here I hold stores and treasures of knowledge. I wish I could find somebody to share it with me.
Yes, I found a few, but one of them, though quite intelligent, was untrustworthy, he would sell his salvation to get hold of the world and its pleasures, he would make religion a pretence to grasp worldly power and wealth, he would make this Blessing of Allah (knowledge) serve him to get supremacy and control over friends of Allah and he would through knowledge exploit and suppress other human beings.
The other person was such that he apparently obeyed truth and knowledge, yet his mind had not achieved the true light of religion, at the slightest ambiguity or doubt he would get suspicious of truth, mistrust religion and would rush towards skepticism. So neither of them was capable of acquiring the superior knowledge that I can impart.
Besides these two I find some other person. One of them is a slave of self and greedy for inordinate desires, which can easily drag him away from the path of religion, the other is an avaricious, grasping and acquisitive miser who will risk his life to grasp and hold wealth, none of these two will be of any use to religion or man, both of them resemble beasts having appetite for food.
If sensible trustees of knowledge and wisdom totally disappear from human society then both knowledge and wisdom will suffer severely, may bring harm to humanity and may even die out.
But this earth will never be without those persons who will prove the universality of truth as disclosed by Allah, they may be well-known persons, openly and fearlessly declaring the things revealed to them or they may, under fear of harm, injury or deaths hide themselves from the public gaze and may carry on their mission privately so that the reasons proving the reality of truth as preached by religion and as demonstrated by His Prophet may not totally disappear.
How many are they and where could they be found? I swear by Allah that they are very few in number but their worth and their ranks before Allah are very high. Through them Allah preserves His Guidance so that they, while departing, may hand over these truths to persons like themselves. The knowledge which they have acquired has made them see the realities and visualize the truth and has instilled into them the spirit of faith and trust. The duties which were decreed as hard and unbearable by them. They feel happy in the company and association of things which frighten the ignorant and uneducated. They live in this world like everybody else but their souls soar to the heights of Divine Eminence. They are media of Allah on this earth and they invite people towards Him. How I love to meet them!"
~ from sayings of Nahj ul Balagha
And (remember) when your Lord said to the Angels:
"Indeed, I am going to place a vicegerent on earth."
~ The Qur'an 2:30
The will of God is done, both in the invisible realm as well as in the visible realm, both in heaven and earth, and that will of placing of vicegerant is carried out in every age, beginning from Adam. As rightly mentioned by Imam Ali that never this earth will be bereft of vicegerents of God, the friends, lovers and saints of God. When that unfortunate day comes when last of such soul is taken away from the earth, it shall come to an end and a new reality of Kingdom will be unveiled. There begins the akhirah, the hereafter.