Allah (swt) addresses the Prophet (saws) telling him that he will be exposed to denial by the skeptics, the hypocrites, the Jews and the polytheists, then:
فَقَدْ كُذِّبَ رُسُلٌ مِّن قَبْلِكَ {so were messengers denied before you,}: The path of calling to Allah (swt) is full of difficulties, so patience is required.
بِالْبَيِّنَاتِ {clear proofs}: Clear evidences and miracles that prove the sincerity of their statement about Allah (swt).
وَالْكِتَابِ الْمُنِيرِ {the enlightening Scripture.}: It means the Torah and the Gospel.