Because that person you call a friend is naturally you want to move around with that person, and you would be affected and influenced from your friend. The Prophet (SAW) once said, that your friend is your iman. A small saying with a great wisdom. Because once you are influenced, your behavior build like your friends, that starts to affect you when you go back to your family. Your liking will become like your friend's liking, because he was your idle, and that is why that person is your friend, so whoever loves you, your children, family members, and who loves you like a hero, would start to follow you, what is learned from your friend. That would also effect your immediate family and other friends. And one day you also want to call your friend at home, to meet with your family, who you always have been talking about, are excited also, and are influenced. 

This is a very important issue, to have right friend, who is a real practicing Muslim. Allah teaches us in the Qur'an about who we should move with in society,

And recite what has been revealed to you (O Muhammad SAW) of the Book (the Qur'ân) of your Lord (i.e. recite it, understand and follow its teachings and act on its orders and preach it to men). None can change His Words, and none will you find as a refuge other than Him. (18:27)

Allah is telling us to read those verses which has come from your Provider by a revelation. And there is no one who can change, and cannot find a better way then the what was sent by Allah.

And keep yourself (O Muhammad SAW) patiently with those who call on their Lord (i.e. your companions who remember their Lord with glorification, praising in prayers, etc., and other righteous deeds, etc.) morning and afternoon, seeking His Face, and let not your eyes overlook them, desiring the pomp and glitter of the life of the world; and obey not him whose heart We have made heedless of Our Remembrance, one who follows his own lusts and whose affair (deeds) has been lost. (18:28)

To keep yourself with those people who call and connects to there provider from morning to evening, and are looking at the will of Allah, what he wants, to obey an follow. Do you want the attractions of this life only? And do not listen to those, who's hearts have been sealed, and have no connection at all with Allah. And those people are going after there desires only, and they are thinking, and work would go far away from the straight path.

O you who believe! Take not My enemies and your enemies (i.e. disbelievers and polytheists, etc.) as friends, showing affection towards them, while they have disbelieved in what has come to you of the truth (i.e. Islâmic Monotheism, this Qur'ân, and Muhammad SAW), and have driven out the Messenger (Muhammad SAW) and yourselves (from your homeland) because you believe in Allâh your Lord! If you have come forth to strive in My Cause and to seek My Good Pleasure, (then take not these disbelievers and polytheists, etc., as your friends). You show friendship to them in secret, while I am All-Aware of what you conceal and what you reveal. And whosoever of you (Muslims) does that, then indeed he has gone (far) astray, (away) from the Straight Path (60:1)

"O you who believe! Take not My enemies and your enemies (i.e. disbelievers and polytheists, etc.)" meaning that Allah is sending us an order to not take His enemies, how can harm Allah? Because Allah loves the practicing Muslims, and they are the enemies of the believers, so then they are the enemies of Allah, because the believers are the one's who follow the laws of Allah., and our enemies. 

"as friends, showing affection towards them, while they have disbelieved in what has come to you of the truth (i.e. Islâmic Monotheism, this Qur'ân, and Muhammad SAW)," who are against Allah his Messenger, and if you call those people as friends, then they would argue and hate you from inside, if you call yourself a believer in front of them, and they would wait for a time to destroy you, as soon as they find the right opportunity to harm you, to harm does not necessarily mean to beat, but financially, or tease you, about your lifestyle becomes the Islamic way. So they would try and change you, what happened, you are smart, so what is making you think that you are over 14 centuries old? Somehow they would give you these messages in jokes, or through different manners, and lets say you are a strong Muslim, then your children would be affected, or your wife. 

"and have driven out the Messenger (Muhammad SAW) and yourselves (from your homeland) because you believe in Allâh your Lord!" Now one should focus what was done to the Prophet (SAW) who never ever harmed anyone, and all the non-believers use to give him there valuable things, in his trust, and would respect him as a noble person. And when they harmed him, so then who we are, how can we be saved from those people? Who we call as friends and are our idles, we adopt all of there fashions, movies, songs, eating habits, wearing habits, talking styles, and all manners ect.

"If you have come forth to strive in My Cause" One should realize, that when we pray five times a day, which is a must, to be a Muslim. We have to leave our work, and make ablution, for who? Naturally for Allah, and we strive to stop our evil and dirty desires. We feel lots of fun in our feelings, but stop ourselves because of the law of Allah. Examples such as this is to strive in Allah's cause.

"and to seek My Good Pleasure, (then take not these disbelievers and polytheists, etc., as your friends)."  One should see, when all the efforts are being put in to as mentioned above, to only seek Allah's good pleasure, one should think if it is worth it to make friendship with those who are the enemies and make jokes about Allah and his Prophet. Do we think that our practicing of Islam and in the same time to make friendship with a non-believer, will it be accepted, or are we earning the anger of Allah?? We do not want to be hypocrites (munafiqs), who would be in bottom of Hell, and they are worse then non-believers. One cannot call non-believers in Allah as friends, we only know them. We have to show in front of the non-believers our best manners, morals, and dealings, as our beloved Prophet use to do.  

"You show friendship to them in secret," In today's world we are focusing modernization, and all the successful non-believers are our idle, and we want to be one of them, or look like them, or act like them in terms of manners and morals, while forgetting the chosen person the Prophet (SAW)'s examples, which is suppose to be followed by those who claim to be Muslim. And this is the order of Allah (SWT).

"while I am All-Aware of what you conceal and what you reveal." Allah (SWT) is very well aware of the fact if our thinking and actions are according to the law of Islam, or not. As we know, all of our actions during the period of our life are recorded as a video would be. 

When some people go to non-believers and act like one of them, in order to keep freindship alive, however once they go back to Muslims, then they act like and talk like a Muslim would, and in there minds they are fooling by themselves that they are balancing there worldly matters and Islam. However in Islam there is no such thing as 50/50, this concept can be understood like in a pale of fresh water, one cannot mix a drop of urine, that water would then be no longer drinkable. Or millions of metric tons of fresh drinking water go to the sea from the river, but mixes there, and it cannot be no longer found.

The same idea applies that a Muslim should not mix with a non-believer in there activities. They should show themselves from there appearance, dealings, and morals what Islam is. The way the Prophet (SAW) use to do. In order to bring those people towards Islam, instead we mix with them, and go towards there path, and call ourselves as "modern" Muslims, and Islam has nothing to do with backwardness or modern, because it is the laws of Allah, either follow it all the way, or leave it and follow Satan. 

 "And whosoever of you (Muslims) does that, then indeed he has gone (far) astray, (away) from the Straight Path" 

Should they gain the upper hand over you, they would behave to you as enemies, and stretch forth their hands and their tongues against you with evil, and they desire that you should disbelieve. (60:2)

"Should they gain the upper hand over you, they would behave to you as enemies," Once one is the control of non-believers in things such as jobs, business dealings, you can see how you are treated because the mercy only comes from Allah and and those who fear him. And that is why in the Holy Qur'an it is mentioned that before you do anything one should ask Allah and make istikhara, in order to be guided to the right path, before starting to deal with them, in any business partnership, or to start to work under them in a job. 

"and stretch forth their hands and their tongues against you with evil," Regardless how close one is to them, but your belief and etiquettes are very different from the non-believers. Basically because, if one is a true believer then the evil person cannot mix. They would try and harm you from either way regardless of there education, because there education is only from this world and not from Allah. 

"and they desire that you should disbelieve."

The wish that you disbelieve, which is not worth it to earn the anger of Allah, who is our creator and provider, and our savior here and in there hereafter.

After reading the contents in the above article, it is important and vital to understand. One can only say to non-Muslim that we know them, but never can trust them as a friend, but our behaviour should be the best with them, so they can take us as an example, and inshallah come towards Islam, and we must remember that in every nation there is good and bad, but we have to follow the laws of Allah, because we do not have enough understanding of who is good and who is bad. So whosoever stays in the boundaries of Allah and his prophet is successful here and in the hereafter, inshallah. 

And incline not toward those who do wrong, lest the Fire should touch you, and you have no protectors other than Allâh, nor you would then be helped^[]. (11:113)