Prefacing an answer to doubts and objections
The opening sentence of verse 38: سُنَّةَ اللَّـهِ فِي الَّذِينَ خَلَوْا مِن قَبْلُ ۚ وَكَانَ أَمْرُ اللَّـهِ قَدَرًا مَّقْدُورًا (a customary practice of Allah in the case of those who have gone before--- And Allah's command is pre-determined by destiny - 38) is a preface to doubts to be encountered in the wake of this marriage, particularly about why so much concern was shown in the case of this marriage despite there being other wives in the household. It was said: 'This is a sunnah of Allah (His customary practice not restricted to Muhammad al-Mustafa t. It has continued to be so in the case of earlier prophets as well, that is, under the dictate of beneficial religious considerations, permission was given for multiple marriages. Well recognized among them are Sayyidna Dawud (علیہ السلام) and Sayyidna Sulaiman Sayyidna Dawud (علیہ السلام) had one hundred wives in his nikah and Sayyidna Sulaiman (علیہ السلام) ، three hundred. Now, if permission came for the Holy Prophet ﷺ to have several marriages under beneficial religious considerations - this nikah being included therein - why should it be taken as something far-fetched? Neither is it contrary to the dignity and status of a prophet and messenger of Allah, nor against the norms of zuhd and taqwa. In the last sentence, it was also said that the matter of nikah (marriage) too, like that of rizq or sustenance, is Divinely decided as to who will be married to whom. That which is written in the eternal destiny has to occur. In this event relating to Sayyidna Zayd ؓ and Sayyidah Zainab ؓ the factors of their mutual temperamental difference, the displeasure of Sayyidna Zayd ؓ and then his resolve to divorce her were all chains of this very creational and destined imperative.