הולך את חכמים יחכם, ורועה כסילים ירוע, "He who walks with scholars will become wise; he who keeps company with fools will come to grief" (Proverbs 13,20).

King Solomon warns people in this verse to try and move within circles of scholars and at the same time to try and avoid keeping company with fools. The reason he uses the expression הולך, is that a person should always walk behind the scholars, become familiar with them, and consider himself as an adjunct to them. He should make of the scholars leaders for his "head.⁠" Anyone who practices this virtue cannot fail to become wise himself.
On the other hand, anyone who habitually mingles with fools will wind up causing harm to his own head, i.e. he will become "broken.⁠" Basically, this verse in Proverbs describes the damage which results from keeping company with fools and the advantage which accrues to a person from the company of scholars. It is a fact that while someone who mingles with the scholars will benefit by such an association, the scholar will not suffer by it at all. This is the reason the Torah has been compared by David to a light (candle), seeing that an unlimited number of people can get light from this candle without the light of the candle becoming dimmed. This is the meaning of Psalms 119, 108 נר לרגלי דברך, ואור לנתיבתי' "Your word is a lamp at my feet, a light for my path.⁠"
Our sages in Yalkut Shimoni (this book was not at the disposal of the author. Ed) comment on this verse in Proverbs that the matter may be compared to someone who enters a perfumery store. His clothing will absorb some of the fragrances in that store although he did not make a purchase of any of the products that are for sale there. In other words, the owner of that store provided a service for the browser without making a sale. Similarly, the mere fact that one is in the presence of scholars results in something rubbing off on those who make a point of being in such company. Solomon describes that the opposite is true when one frequents the haunts of fools. Not only is their presence not beneficial, but it is even harmful to those who are not of their ilk.
The expression כסילים which Solomon applies to these fools are people who deliberately choose negative virtues, indulge in physical pleasures as their main purpose in life and who at the same time despise and ridicule people concerned with moral/intellectual pursuits. Such people do not qualify for admonition as they belong to one of the three categories of people who are not to be admonished. They are 1) כסילים, fools, 2) לצים, scoffers, 3) רשעים, wicked people. Concerning category one Solomon said (Proverbs 23,9) "do not speak to a fool; he will disdain your sensible words.⁠" Concerning the scoffer, Solomon said (Proverbs 9,8) "do not admonish the scoffer lest he hate you.⁠" Concerning the wicked, Solomon said (Proverbs 9,7) "rebuking a wicked person one hurts oneself.⁠" Just as the very company of scholars is like an open invitation to serve the Lord, so the company of the other types of people we mentioned is like an invitation to reject the service of the Lord. The Torah writes in Deut. 7,4 "for he will lead astray your son (grandson) from following Me. The Torah spoke about the results of intermarriage of a Jewish girl with a Gentile. Although, technically speaking, the children of such a union will be Jews, the influence of the Gentile father and his family will estrange them to Judasim.
For all the above considerations David commenced his Book of Psalms with praise for the people who resist keeping company with the habitual sinners, and who instead make the Torah of G-d the object of their ambition, preoccupying themselves with it both by day ad by night (Psalms 1,1-2).
Solomon followed in the footsteps of his father when he commenced the Book of Proverbs (1,8) with the words שמע בני מוסר אביך, "listen to the instruction of your father my son; etc.⁠" He continued immediately by warning that we should not expose ourselves to the seductive words of the wicked (1,10).
Our patriarch Avraham made every effort to observe the eventual laws of the Torah and the sacrificial services; our sages illustrated this when they said (Yoma 28) that he even observed such rabbinic ordinances as עירוב תבשילים, ensuring that he had cooked and baked food in the house for the Sabbath which follows on the heels of a festival so that preparation of food on the festival itself would not be viewed as exploiting a day when work is forbidden to prepare for the Sabbath. Avraham faced the dilemma of keeping away from wicked people, people who were the cause of truly free choice of worship having become impossible. Once you have become a true heretic (compare Maimonides Hilchot Teshuvah) you are not given a chance to repent). This is why G-d told him to move away from such people so that he would not become infected by them. G-d sent him away from his land, his birthplace to a land which He was going to show him (once he had set out to leave his home).
According to Tanchuma 3 on Lech Lecha, Avraham was not aware of the stench caused by the people amongst whom he lived as his environment was similar to a graveyard which had been sprinkled with a bottle of spikenard oil which neutralized the stench which emanates from there. How did G-d deal with this problem? He took Avraham from place to place and acquainted him with the different smells of the universe. In this manner Avraham was able to appreciate what was wrong in the world, and he would be trained not to become overwhelmed by the stench caused by the lifestyles of his contemporaries. Then came the point when G-d said to Avraham: "remove yourself from them and do not become dirtied by them.⁠" This is the meaning of the words לך לך, i.e. "it is time that you by yourself.⁠" The repetition of the letters לך לך allude to the word לכלך, dirt. G-d did not want him to become dirtied by his surroundings.
This was the first of the ten trials Avraham had to undergo; he successfully coped with all of them. The final and greatest trial was when G-d told him to offer up his son Yitzchak on Mount Moriah. At that time G-d again introduced the trial with the words לך לך in order to compare his first trial to his last trial. The commandment of which the Torah speaks here at the beginning of chapter 12 was issued while Avraham was in Charan as this was his country and his birthplace. Concerning that place Avraham said later (23,2 when he instructed Eliezer to get a wife for Yitzchak): "but go only to my country and to my birthplace!⁠" It was certainly a great trial for him to leave his country and the place he had been born and raised in, the place where he had dwelled with his whole family, and to go to an entirely unknown country.
Remember that prior to G-d's communication to Avraham telling him to move away from home, it would have been appropriate for the Torah to tell us something about Avraham's virtues, just as the Torah had done before it reported that G-d issued commands to Noach before him. We must assume that the reason the Torah did not do so was because it had already hinted previously that Avraham was a person of exceptional qualities when the Torah referred to אור כשדים, as we explained on 11,28.