First of all, let me present to you some other translations of the same verse:
Muhammad is the messenger of Allah. And those with him are hard against the disbelievers and merciful among themselves. Thou (O Muhammad) seest them bowing and falling prostrate (in worship), seeking bounty from Allah and (His) acceptance.... -- M. M. Pickthall
Muhammad is the Messenger of Allah, and those with him are firm of heart against the unbelievers, compassionate among themselves; you will see them bowing down, prostrating themselves, seeking grace from Allah and pleasure... -- Shakir
Secondly, this surah was revealed when Muslims were at war with the Kafirs of Mecca. Ibn Khatir said:
This honorable Surah was revealed after the Messenger of Allah returned from the area of Al-Hudaybiyyah, during the month of Dhul-Qa`dah, in the sixth year of Hijrah.
Thirdly, a disbeliever is not a non-Muslim. A disbeliever is a person who rejected Islam even after receiving the massage of Islam in its true form.
How can the Muslims be "forceful" among disbelievers and "merciful" among themselves in the modern world which is referred to as the "Global Village"?
The Arabic word “ashidda” means strong or firm. Forceful doesn't sound like a correct translation. As far as I know, there are different views regarding the interpretation of this verse. Islamnewsroom wrote regarding its interpretation:
The Arabic word "ashidda" does not mean ruthless, but strong and firm. Ruthless is an unacceptable translation. Translations of ashidda:
Pickthall: hard; Yusuf Ali: strong; Daryabadi: stern; Khan-Hilali: severe; F. Malik: strong; Shakir: firm of heart; Arberry: hard; Irving: strict Also, the disbelievers being referred to in these verses are the those who persecuted and attacked the Muslims. Shaykh Fawzee Al-Atharee said the following:
"And similarly the disbeliever, if he has good character with us and good manners with us and good way and treatment with us, then we have good manners with him, good behaviour with him, good way with him and good treatment of him. And if his manners are bad and his behaviour is bad [i.e. abusive and cruel], then we treat him with accordance to how he is treating us. This is something permissible in the legislation. But the Prophet s.a.w.s. has indicated very clearly in all the narrations that have been brought and throughout his life, that there must be a matter of balance and to be just. And that is in dealing with the people of disbelief and also in dealing with those who have faith."
The Muslims were commanded to stand up for their religion and defend themselves against the persecution of the disbelievers. Again, if we examine the historical context, we also find that this is referring to those who attacked the Muslims continuously. So verses apply in a situation similar to the historical context.
Since this verse mentions the companions of the Prophet Muhammad (peace be upon him) and praises their path, let us examine some narrations about the companions. Musab bin Umair was a notable companion of the Prophet Muhammad (peace be upon him). He was sent to Madinah to share the message of Islam with the people living there. One incident of his related as follows:
"Once Musab and Sad were sitting near a well in an orchard of the Zafar clan. With them were a number of new Muslims and others who were interested in Islam. A powerful notable of the city, Usayd ibn Khudayr, came up brandishing a spear. He was livid with rage. Sad ibn Zararah saw him and told Musab: "This is a chieftain of his people. May God place truth in his heart." "If he sits down, I will speak to him," replied Musab, displaying all the calm and tact of a great daiy. The angry Usayd shouted abuse and threatened Musab and his host. "Why have you both come to us to corrupt the weak among us? Keep away from us if you want to stay alive." Musab smiled a warm and friendly smile and said to Usayd: "Won't you sit down and listen? If you are pleased and satisfied with our mission. accept it and if you dislike it we would stop telling you what you dislike and leave." "That's reasonable," said Usayd and, sticking his spear in the ground, sat down. Musab was not compelling him to do anything. He was not denouncing him. He was merely inviting him to listen. If he was satisfied, well and good. If not, then Musab would leave his district and his clan without any fuss and go to another district. Musab began telling him about Islam and recited the Quran to him. Even before Usayd spoke, it was clear from his face, now radiant and expectant, that faith had entered his heart. He said: "How beautiful are these words and how true! What does a person do if he wants to enter this religion?" "Have a bath, purify yourself and your clothes. Then utter the testimony of Truth (Shahadah), and perform Salat. Usayd left the gathering and was absent for only a short while. He returned and testified that there is no god but Allah and that Muhammad is the Messenger of Allah."
Islamicstudies.info interprets it as:
The companions (of the Prophet) are hard against the disbelievers: They are not such that the disbelievers may mold them as they like. They can neither be cowed nor purchased by any inducement. The disbelievers have no power to turn them away from the great objective for the sake of which they have joined and followed the Prophet (peace be upon him) even at the cost of their lives.