مَا كَانَ عَلَى النَّبِيِّ مِنْ حَرَجٍ فِيمَا فَرَضَ اللَّهُ لَهُ سُنَّةَ اللَّهِ فِي الَّذِينَ خَلَوْا مِنْ قَبْلُ وَكَانَ أَمْرُ اللَّهِ قَدَرًا مَقْدُورًا ﴿۳۸﴾ الَّذِينَ يُبَلِّغُونَ رِسَالَاتِ اللَّهِ وَيَخْشَوْنَهُ وَلَا يَخْشَوْنَ أَحَدًا إِلَّا اللَّهَ وَكَفَى بِاللَّهِ حَسِيبًا ﴿۳۹﴾

﴾38﴿ Maa kaana 'alan nabiyyyi min harajin feemaa faradal laahu lahoo sunnatal laahi fil lazeena khalaw min qabl; wa kaana amrul laahi qadaram maqdooraa
﴾39﴿ Allazeena yuballighoona Risaalaatil laahi wa yakhshaw nahoo wa laa yakkhshawna ahadan illal laah; wa kafaa billaahi Haseebaa

﴾38﴿ There is no difficulty upon the Prophet, peace and blessings be upon him, in carrying out what Allah, the Exalted, has ordained for him. [This is] the way of Allah among those who passed before, and the command of Allah, the Exalted, is a decree determined
﴾39﴿ These are the ones who convey the messages of Allah, the Exalted, and fear Him, and they do not fear anyone except Allah. And sufficient is Allah, the Exalted, as a Reckoner

[38] This is another address to the Prophet (May Allah bless him and give him peace), but phrased in the third person (gha’ib form) as a sign of respect and honor.
Connection to the previous verses: Since there was fear of public criticism regarding the marriage to Zaynab, this verse serves as encouragement — that this marriage was a means of fulfilling Allah’s command to His creation, particularly in abolishing a polytheistic custom (i.e., considering the wife of an adopted son as forever forbidden).
Thus, it was not permissible for the Prophet to feel any hesitation or discomfort in carrying out this command.
"Sunnata Allāh" — refers to the divine method followed with all previous prophets, either:
in terms of freedom and boldness in delivering the message without fear,
or in terms of the wide scope of marriage allowed to previous prophets such as Dāwūd and Sulaymān (peace be upon them).
The word “sunnah” here has an implied “kāf” (comparison) before it — as in “ka-sunnati Allāh” — meaning “like the way of Allah”.
In the previous verse, the phrase "maf‘ūlan" was used, because it referred to the actual marriage to Zaynab, which had already been fulfilled.
In this verse, "qadaran" is used, implying “divine decree”, because it refers to the preordained nature of the command — and
"maqdūran" is for emphasis: “a fixed and unchangeable destiny”, meaning there can be no alteration or resistance to what Allah has decreed.
[39] This phrase is a description or substitute (badal) for "alladhīna khalaw min qablu" — referring to the prophets who came before, and it highlights them with three qualities.
"Wa kafā bi-llāhi ḥasīban" — this is a warning to those who object to the prophets or their actions.
It means that Allah is sufficient to take account of them, and He will hold them accountable for their objections and the reasons behind them.
It emphasizes that no one has the right to criticize the prophets, and that Allah alone is the judge and reckoner over such matters.