And you don’t weaken your heart in meeting any enemy in the war if you are suffering hardship; then indeed they are also suffering hardship just like you are suffering, while you are expecting something from Lord Allah that they are not expecting, and Allah is the All-Knowing, the Wise.
This verse is revealed to encourage the followers for joining battles against the disbelievers during Messenger's time. But today there is no group of believers anywhere in the world. As commanded through verses 9: 73, the odd believer is commanded to do Jihad with Adhikr against the Fujjar who are repeatedly hiding and rejecting Lord’s Book. They should also have to propagate Adhikr throughout the world to utilize It as the Balance and Trust to keep the universe in its equilibrium and to form the harmony of mankind. See explanation 3: 139; 4: 91 and 9: 73.