The purpose in previous verses was to point out to some ugly traits of the hypocrites, though their punishment of being in Hell with disbelievers was also mentioned as a corollary to another subject.
From this stage onwards, the purpose is to state their punishment clearly. Since the inherent effect of such impending punishment generates a sense of fear in a good-natured person which usually becomes the reason for early repentance, therefore, exemption from punishment has been promised to those who repent alongwith the incentive of good reward for them.
The Meaning of sincerity
The statement: وَأَخْلَصُوا دِينَهُمْ (Make their Faith pure for Allah) in verse 146 shows that a deed in order to be acceptable with Allah has to be free of hypocrisy and exclusively for His sake and pleasure, for Muslim jurists have enunciated the meaning of Mukhlis (translated with the weaker equivalent 'sincere' ) as follows:
اَلَّذِی یَعمَلُ للہ لَا یُحِبُّ اَن یُّحمَدَہُ النَّاسُ عَلَیہِ
A sincere person is one who acts for Allah alone and does not like that people praise him for it. (Mazhari)