أُوْلَـيِكَ هُمُ الْكَافِرُونَ حَقًّا
They are in truth disbelievers.
meaning, their disbelief in the Prophet they claim to believe in is clear. This is because their claimed faith in a certain Messenger is not true, for had they truly believed in him, they would have believed in other Messengers, especially if the other Messenger has a stronger proof for his truthfulness. Or at least, they would have strived hard to acquire knowledge of the truth of the other Messenger.
Allah said,
وَأَعْتَدْنَا لِلْكَافِرِينَ عَذَابًا مُّهِينًا
And We have prepared for the disbelievers a humiliating torment.
This is just punishment for belittling the Prophets whom they disbelieved in, by ignoring what the Prophet brought to them from Allah, and because they are interested in the insignificant possessions of this world. Or, their behavior could be the result of their disbelief in the Prophet after they were aware of his truth, just as the Jewish rabbis did during the time of Muhammad, the Messenger of Allah. The Jews envied the Messenger because of the great Prophethood that Allah gave him, and as a consequence, they denied the Messenger, defied him, became his enemies and fought against him. Allah sent humiliation upon them in this life, that shall be followed by disgrace in the Hereafter,
وَضُرِبَتْ عَلَيْهِمُ الذِّلَّةُ وَالْمَسْكَنَةُ وَبَأوُوْاْ بِغَضَبٍ مِّنَ اللَّهِ
(And they were covered with humiliation and misery, and they drew on themselves the wrath of Allah), (2;61) in this life and the Hereafter.
Allah's statement