The holy sentence which says: “…The Truth has indeed come to you from your Lord.
The holy sentence which says: “…The Truth has indeed come to you from your Lord...” signifies: by means of the revelations and exhaustive proofs it has been proved to you that what has been passed to you is an authentic and genuine truth which leaves no room for any sort of skepticism. Thus, be firm in your beliefs in which case you should have no doubts, not refuting and denying the Divine verses, and continue your course.
Many a time if skepticism remains unchallenged, it will lead to refutation. The verse says: “Nor be of those who belied the Signs of Allah, (for) then you shall be of the losers.” All investigation and analysis that had been applied to skepticism in the previous verse, may equally propound here as well, for refutation is worse than skepticism. There have been numerous verses and traditions which inform of the certainty the Prophet (S) possessed.
“Even if every Sign come unto them, until they see the painful chastisement.” Allah tells the Prophet (S), here, that there is a group among his opponents who are fanatic and obstinate and who cannot be expected to become believers. They have become so brainwashed in their thinking, and have been led astray to such an extent that they have lost their human consciences, becoming individuals who may not be impressed or influenced.
However, explaining the subject with this connotation, the Qur’an says that Allah’s commandment had been proven and was unequivocal to them, though they will not become believers.