Allah demeans the unbelievers in this life

Those who mock Allah's religion and revelation, as well as His prophets and those who follow them, have always existed. Incapable of praising Allah's power and greatness, they live heedless lives and overlook the fact that they will be punished for their deeds. They continue to hold this attitude, even though the Qur'an tells them that the punishment they regard as being far in the future is, in reality, very close at hand:

They deny the truth each time it comes to them, but news of what they were mocking will certainly reach them. (Surat al-An'am, 5)

Messengers before you were also mocked, but those who jeered were engulfed by what they mocked. (Surat al-Anbiya', 41)

… every time some nobles of his people passed him by, they ridiculed him. He [Nuh] said: "Though you ridicule us now, we will certainly ridicule you as you do us. You will soon know who will receive a punishment that disgraces him and find unleashed against himself an everlasting punishment." (Surah Hud, 38-39)

There is no doubt that these people will be punished for their sins in the Hereafter. However, this punishment also reaches them while they are still in this world. They mock the believers and the prophets sent by Allah, and Allah mocks them. Allah makes this absolutely clear:

But Allah is mocking them and drawing them on as they wander blindly in their excessive insolence. (Surat al-Baqara, 15)

By misusing the time allotted to them, the unbelievers fall into a terrible trap. Throughout their lives they struggle against the Qur'an's morality, Allah's prophets, and the believers, thinking that they will suffer no negative consequences. In fact, no matter how arrogant they may be in this life, they will die and be buried whenever Allah wills this to happen. Allah withdraws the property of which they are so proud and leaves their bodies to rot beneath the ground. All of this is inescapable - they will die just like everybody else. Their mortality and inability to escape death are the greatest proofs of their desperate position.