The verse says:
"O you who have believed, what is [the matter] with you that, when you are told to go forth in the cause of Allah, you adhere heavily to the earth? Are you satisfied with the life of this world rather than the Hereafter? But what is the enjoyment of worldly life compared to the Hereafter except a [very] little." (9:38)
This verse has a story so let's first put it in its context:
"O you who have believed, what is [the matter] with you that, when you are told to go forth in the cause of Allah, you adhere heavily to the earth? Are you satisfied with the life of this world rather than the Hereafter? But what is the enjoyment of worldly life compared to the Hereafter except a [very] little.
If you do not go forth, He will punish you with a painful punishment and will replace you with another people, and you will not harm Him at all. And Allah is over all things competent.
If you do not aid the Prophet – Allah has already aided him when those who disbelieved had driven him out [of Makkah] as one of two, when they were in the cave and he said to his companion, "Do not grieve; indeed Allah is with us." And Allah sent down his tranquility upon him and supported him with angels you did not see and made the word of those who disbelieved the lowest, while the word of Allah – that is the highest. And Allah is Exalted in Might and Wise.
Go forth, whether light or heavy, and strive with your wealth and your lives in the cause of Allah. That is better for you, if you only knew." (9:38-41)
When was that verse revealed?
Taken from the website: Al-Islam.org
The verse was revealed during the battle of "Tabuk". "Tabuk" was a region in the northern borders of Hijaz "Saudi Arabia" around 778 miles from Medinah.
The rapid penetration and expansion of Islam in the Arabian Peninsula and the brilliant conquests by the Muslims in the Hijaz were being noticed in areas beyond the Hijaz (i.e. Syria). In those times Syria was one of the colonies of the Eastern Roman Empire. Its capital was Constantinople. The Roman emperor decided to stand in the face of the expansion of Islam and started giving weapons and supplies to tribes in the northern borders between Hijaz and Syria like Ghasan, Lakhm and others
In those days Rome was the only powerful adversary of Iran and possessed the greatest political and military strength. It was very proud on account of the victories which it had achieved against Iran and the defeat which it had inflicted on the Iranian army.
The Roman army, the most highly equipped army at that time, encamped in the frontier strip of Syria. The tribes residing in the border areas (like the tribes of Lakham, 'Amilah, Ghassan and Jazam) also joined them and the vanguard of the army advanced up to Balqa'
News about the encampment of a group of the Roman soldiers in the frontier strip of Syria reached the Prophet through the caravans, which were travelling between the Hijaz and Syria in connection with trade. He found no alternative except to give a reply to the aggressors with a big army in order to protect the Islamic state from the sudden attack prepared for by the Romans.
Prophet Muhammad, peace and blessings be upon him, ordered the Muslims to prepare for battle. The Battle of Tabuk was the best occasion on which the self-sacrificing persons and the pretenders and hypocrites could be recognized, because general mobilization was ordered when the weather was very hot, the distance they had to travel to reach "Tabuk" was long and the business community of Madina was ready to harvest the palm-dates. Refusal of some of them, on various pretexts, to take part in the battle cast off the veil from their real faces and Qur'anic verses were revealed condemning their action.
The army of Islam arrived in the area of Tabuk in the beginning of the month of Sha'ban 9 A.H. However, no trace of the Roman army could be seen there. It appears that the commanders of the Roman army became aware of the numerical strength of the Muslim soldiers and their bravery and unparalleled self-sacrifices so they returned where they came from.
Prophet Muhammad, peace and blessings be upon him, personally contacted those frontier rulers, who belonged to areas adjoining Tabuk, and concluded non-aggression treaties with them, subject to certain conditions. As regards areas lying at a greater distance from Tabuk he sent deputations to the rulers concerned so that better security could be ensured for the Muslims.
He also contacted the Rulers of Aylah, Azri'at and Jarba' and non-aggression pacts were concluded between the parties. Aylah is a coastal city situated on the coast of the Red Sea and is at some distance from Syria. Its ruler named Yuhanna (John) son of Rowbah came from his capital to Tabuk, wearing a golden cross round his neck. He presented a white mule to the Prophet and expressed his obedience to him. The Prophet appreciated his gesture and also gave him a present in return.
The ruler decided to remain a Christian and agreed to pay three thousand Dinars per year as jizyah(tribute) and also to receive every Muslim who passed through the region of Aylah. A pact on the following lines was signed by the parties: "This is a non-aggression pact from the side of Allah and His Prophet, Muhammad for Yuhanna and the residents of Aylah. According to this pact all their means of transport whether by sea or by land and all the persons belonging to Syria, Yemen and the islands, who may be with them, shall be under the protection of Allah and His Prophet.
However, if anyone of them violates the rule his wealth shall not save him from punishment. All sea routes and land routes are open for them and they are entitled to frequent them''. This pact shows that if a nation co-operated with the Muslims in a peaceful manner it was provided all the facilities, and its security was also guaranteed by them.
The Prophet also concluded pacts with the frontiers-men like the people of Azri'at and Jarba' whose lands had great strategic importance, and thus ensured the safety of the Islamic territories from the northern side.
This battle was called the battle of hardship (khazwa al-osra), due to the hardships the Muslims had to endure on their way to the Syrian borders.
An insight in the Linguistics of the verses
1- The word " go forth" in this verse is the translation of the word "ANFERW" which is used when someone is motivating you to respond to aggression or provocation you are subjected to. So it reflects that the action is for self defense NOT an act of aggression initiated by Muslims.
2- " adhere heavily" in this verse is the translation of the word "ATHAKALTOM" which is used when you imitate incapability. It is a prove the some Muslims were reluctant to go to this war because
3- In the verse (9:39)GOD is threatening the reluctant Muslims, who were reluctant to defend themselves from an approaching danger that if they don't they will be punished. I don't actually understand why does that feel offensive to some people. If today your country, no matter how lenient, is threatened and an order is given to your soldiers to prepare for a war to defend their and their families existence, what do you think the reaction of your military leaders will be if some of them show reluctance. For a Muslim a threat from GOD is enough because he believes that God is capable of punishing him.
4- In the verse (9:40) God is giving the reluctant Muslims a real-life example, that they personally witnessed, that HE is capable of aiding HIS prophet to victory. The example was while the Prophet, peace and blessings be upon him, was emigrating to Medinah right after the people of Mecca conspired to kill him. Our Noble Prophet, peace and blessings be upon him, emigrated with only his friend Abu Bakr secretly and were about to be discovered had it not been for the mercy of GOD and HIS protection for HIS prophet. And notice here the word "driven", which means that our Noble Prophet, peace and blessings be upon him, was forced to leave Mecca whose people conspired to kill him.
5- In the verse (9:41) GOD is ordering Muslims to 'go forth whether light or heavy'. (light) here means those who were willing to participate in the war while (heavy) here means those who will participate but with difficulty.
Notice also the word " strive" which shows difficulty and that you are fighting against someone who is ready and prepared to fight back which means the battle of "Tabuk" was no surprise to the Romans and that it was not an act against civilians but a war against soldiers who were getting prepared to fight you.
I don't see why some people consider this a violent verse since it was revealed in an occasion of war where the Muslims were facing the strongest army in the world. I can never accept that ANY leader will do anything other than to motivate his soldiers to defend themselves and warns them against any display of reluctance.