(Verily, those who live in awe for fear of their Lord;) means, even though they have reached the level of Ihsan and have faith and do righteous deeds, they are still in awe of Allah and fear Him and His hidden plans for them, as Al-Hasan Al-Basri said, "The believer combines Ihsan with awe, while the disbelievers combine evil deeds with a sense of security."
وَالَّذِينَ هُم بِـَايَـتِ رَبَّهِمْ يُؤْمِنُونَ
(And those who believe in the Ayat of their Lord;) means, they believe in His universal and legislative signs, as Allah says about Maryam, peace be upon her:
فَتَقَطَّعُوا أَمْرَهُم بَيْنَهُمْ زُبُرًا But they split up ways from one another (dividing themselves) into factions - 23:53). The word زُبُر is the plural of زُبُور meaning a book, and the verse would mean that Allah had commanded all prophets and their followers to adhere to the one and only faith revealed by Him in all matters relating to the basic principles and beliefs. But the followers of different prophets split up into groups and sects and each one of them chose a different way of life and adopted a different book in which the beliefs of each group and sect were recorded. Sometimes زبر is used for the plural of زُبرَہ (zubrah) meaning "fragment" or "group". This meaning is more appropriate here and the meaning of the verse would be that these people were divided into sects even in the matter of fundamental beliefs of their religion. It should be noted that the difference of opinion among the mujtahidin (competent Shari` ah Scholars) in some minor issues is not included in this division which is condemned in this verse, because these differences do not cause a division of the religion, nor do the people maintaining these differences become separate sects. Giving these interpretative and subsidiary differences a sectarian colour is the height of ignorance and no religious scholar would support it.
Tazkirul Quran
Maulana Wahiduddin KhanOn ayahs 55–61
When the religion of God is revived in its true spirit, it instills the fear of God in people’s minds but when religion loses its true spirit, it becomes a mere source of boasting and pride for its adherents. This is the time when men of religion split into a number of groups. Each group chooses for itself that aspect which feeds its pride. Groups which feed on pride are always many in number, while the religion of the God-fearing is always one. An absence of fear breeds a diversity of opinions, while a God-fearing mentality leads to uniformity of opinion. In the present world, man is being put to test. During the period of respite allowed to an individual or a group at God’s behest, all the amenities of life are provided. On account of this, negligent people think that whatever they are doing is right and that, if they had been wrong, their possessions and all comfort and convenience would have been snatched away from them. But, by God’s method, a man’s possession are taken away from him, not on his flouting God’s will during the trial period, but in the world hereafter.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.