(only for the Hour that it shall come upon them suddenly while they perceive not) means, for it is real and will inevitably come to pass, and these negligent people are unprepared for it. When it comes, it will catch them unawares, and on that Day they will feel the utmost regret when regret will not benefit them in the slightest and will not afford them any protection.
(Friends on that Day will be foes one to another except those who have Taqwa.) means, every friendship that exists for a purpose other than for the sake of Allah will turn to enmity on the Day of Resurrection, except for that which is for the sake of Allah, which will last forever. This is like the statement of Ibrahim, peace be upon him, to his people:
The only real friendship is that which is in the sake of Allah
الْأَخِلَّاءُ يَوْمَئِذٍ بَعْضُهُمْ لِبَعْضٍ عَدُوٌّ إِلَّا الْمُتَّقِينَ (Friends, on that day, will become enemies to one another, except the God-fearing 43:67). This verse tells us plainly that the friendly relations in which we take so much pride in this world, and for which we don't even care about halal (permitted) and Haram (unlawful), will be of no use on the Day of judgment, rather they will turn into enmity. In this connection, Hafiz Ibn Kathir has reproduced a discourse of Sayyidna ` Ali ؓ narrated by ` Abdur Razzaq in his Musannaf and by Ibn Abi Hatim regarding two Muslim friends and two Non-Muslim friends. One of the Muslim friends died and when he was given the glad tidings of Paradise, he recollected his friend and supplicated in his favour: "0 Allah! That friend of mine used to advise me to obey You and to obey the Holy Prophet ﷺ ، he used to direct me towards virtues and to prevent me from vices, and kept on reminding me that one day I would have to meet You. So 0 Allah! Do not misguide him after me, so that he may also see the scenes of Paradise as You have shown to me, and be pleased with him, as you have been with me." In reply, it will be said to him, "Do not worry, if you know what reward I have stored for your friend, you will weep less and laugh more." Later, when the friend will also have died, both the souls will get together and Allah Ta` ala will direct them that each one of them should praise the other. Thereupon, each one of them will say about the other that he is the best brother, best companion and the best friend.
Here ‘wisdom’ means the spirit of religion and ‘straight path’ means the upholding of the virtues that are mentioned in the verse, namely, fear and worship of God, prayer to Him and obedience to the Prophet. This is the real religion. What the Jews did at a later stage was to lose the spirit of religion and indulge in hair-splitting over the basic principles of religion. Due to these totally contrived additions, differing sects developed among them. One sect laid stress on one controversial issue, another laid stress elsewhere. In this way, with them, one religion turned into several religions. Jesus Christ was sent to the Jews to tell them that the really important aspect of religion was its spirit and not form; and also to inform them that they would achieve salvation on following the true religion sent by God and not that religion which they had themselves devised. Jesus told them that the real religion was based on the fear of God, and that they should become worshippers of the one and only God and follow the example of the Prophet in everyday affairs. Beyond this, whatever innumerable problems they had created by their futile discussions and hair-splitting arguments were their own self-made additions. They were advised to give up all these additions and be steadfast in their adherence to the real religion. All these exhortations made by Jesus exist in the Bible even today.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.