87
"Who will be lenient towards the Believers" means that they will never use force against the Believers and will never employ their intelligence, ability, influence, wealth, power or anything else to suppress or oppress them or inflict loss on them. The Muslims will always find such persons to be mild, kindly, amiable and sympathetic.
"..........but stern towards the disbelievers" means that a Believer will be firm, strict, uncompromising and militant towards the opponents of Islam by virtue of his firm faith, sincere religious sense, strict principles, strong character and God-given intelligence. Whenever the disbelievers will come in conflict with him, they will find that a Believer can neither be bought nor coerced because he is so uncompromising in his Islamic principles that he would rather die than yield.
88
That is, they will fearlessly follow the Way of Allah and act upon His commandments, and declare to be right what is right, and wrong what is wrong, according to it, and will not mind in the least the opposition, the censure, the criticism, the objections, the derision and ridicules of their opponents. They will boldly follow the Way of Islam which they sincerely believe to be right, even if the popular opinion is against Islam and they are exposed to the ridicule, derision and taunts of the world.
