(Say: "O Allah! Possessor of the power, You give power to whom You will, and You take power from whom You will, and You endue with honor whom You will, and You humiliate whom You will. In Your Hand is the good. Verily, You are able to do all things. You make the night to enter into the day, and You make the day to enter into the night, You bring the living out of the dead, and You bring the dead out of the living. And You give wealth and sustenance to whom You will, without limit.) 3:26-27 The meaning of "merging" the night into the day and the day into the night is that the one encroaches upon the other, and vice versa. Sometimes the night is long and the day is short, as in winter, and sometimes the day is long and the night is short, as in summer.
In an earlier verse it has been mentioned that Allah Ta’ ala helps those who are wronged unjustly وَإِنَّ اللَّـهَ عَلَىٰ نَصْرِهِمْ لَقَدِيرٌ (Allah is powerful to give them victory - 22:39) Some people bear their sufferings patiently and do not seek vengeance from their oppressors, but there are others who retaliate and serve a full measure of retribution on their oppressors which should, therefore, place them both on even terms as being quits. But if the oppressor, incensed at the retaliation, attacks him again, then this person once again becomes the victim of oppression. This verse promises Allah's help for such a person also. On the other hand there are several verses which promise Allah's goodwill to those Muslims who bear their sufferings with patience and equanimity and do not seek vengeance from their oppressors. Some of these verses are:
The system of this world, in its silent language, goes on teaching us a great lesson. Here, again and again, we see the phenomenon of the darkness of the night coming and enveloping the light of the day. Here, every day, the day dawns and dispels the darkness of the night. By analogy, if a group or community is enjoying pomp and glory, it should not harbour the misunderstanding that its pomp and glory will never come to an end. Similarly, if a group or community is oppressed, it should not think that it will remain oppressed forever. God who, in the realm of the heavens, causes the light to be plunged into darkness, and who then restores it, can certainly cause similar events to occur in the world of human beings also. There is no power that can prevent Him from doing so.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.