Ya ayyuha allatheena amanoo ittaqoo Allaha waaminoo birasoolihi yu'tikum kiflayni min rahmatihi (surah Hadid: 28)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(57:28) Believers, have fear of Allah and believe in His Messenger, *55 and He will grant you a two-fold portion of His Mercy, and will appoint for you a light whereby you shall walk; *56 and He will forgive you. *57 Allah is Most Forgiving, Most Compassionate.

Yaaa ayyuhal lazeena aamaanut taqullaaha wa aaminoo bi Rasoolihee yu`tikum kiflaini mir rahmatihee wa yaj`al lakum nooran tamshoona bihee wa yaghfir lakum; wallaahu Ghafoorur Raheem

*55) The commentators differ in the explanation of this verse, One group says that the address here is directed to the people who believed in the Prophet Jesus. It is being said to them, "Believe in the Holy Prophet Muhammad (upon whom be Allah's peace and blessings) now; for this you will be given a double reward, one reward for believing in the Prophet Jesus (peace be upon him) and the other reward for believing in the Prophet Muhammad (upon whom be Allah's peace and blessings). The second group says that the followers of the Holy Prophet Muhammad (upon whom be Allah's peace and blessings) are being addressed. They are being admonished to the effect: "Do not rest content with your verbal affirmation of the Faith only, but you should believe sincerely and truly For this you will be given . a double reward: one reward for giving up disbelief and turning to Islam, and the second reward for believing sincerely in Islam and remaining steadfast to it. "The first commentary is supported by vv. 52-S4 of Surah AI-Qasas, and furthermore by the tradition reported by Hadrat Abu Musa al-Ash'ari, according to which the Holy Prophet (upon whom be peace) said: "There are throe men who will get a double reward, one of them is a person from among the followers of the earlier Books who believed in this earlier Prophet and then believed in the Prophet Muhammad (upon whom be Allah's peace)." (BukhAri Muslim). The second commentary is supported by verse 37 of Surah Saba, which says that the righteous believers will have a double reward. From the point of view of argument both the commentaries are equally weighty. However, considering the theme that follows, one feels that the second commentary is more in keeping with the context here; and in fact the whole theme of this Surah, from beginning to end, supports this very commentary. From the beginning of this Surah- the addressees are the people who had entered Islam after affirming the Prophethood of the Holy Prophet and it is they whom the Surah invites to believe sincerely and truly and not merely verbally with the tongue
*56) That is, "He will bless you with such a light of knowledge and vision in the world by which you will be able clearly distinguish at every step the straight way of Islam from the crooked paths of ignorance in different matters of life, and in the Hereafter He will grant you the Light that has been mentioned in verse 12 above.'
*57) That is, "He will forgive you your errors that you may happen to commit due to human weaknesses in spite of your sincere efforts to fulfil the demands of the Faith, and will also forgive those sins of yours that you had committed in the pre-Islamic days of ignorance."