Qadr of Allah (SWT)
يَـٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ لَا تَكُونُوا۟ كَٱلَّذِينَ كَفَرُوا۟ وَقَالُوا۟ لِإِخْوَٰنِهِمْ إِذَا ضَرَبُوا۟ فِى ٱلْأَرْضِ أَوْ كَانُوا۟ غُزًّۭى لَّوْ كَانُوا۟ عِندَنَا مَا مَاتُوا۟ وَمَا قُتِلُوا۟ لِيَجْعَلَ ٱللَّهُ ذَٰلِكَ حَسْرَةًۭ فِى قُلُوبِهِمْ ۗ وَٱللَّهُ يُحْىِۦ وَيُمِيتُ ۗ وَٱللَّهُ بِمَا تَعْمَلُونَ بَصِيرٌۭ
O believers! Do not be like the unfaithful1 who say about their brothers who travel throughout the land or engage in battle, “If they had stayed with us, they would not have died or been killed.” Allah makes such thinking a cause of agony in their hearts. It is Allah who gives life and causes death. And Allah is All-Seeing of what you do. [3:156]
Have you ever wondered if doing something different would've changed the outcome of a situation? For example, let's say you're on a road trip and you hit the car in front of you. You might ask yourself "If I had been paying better attention while driving I might not have hit the car." Yes, this could be true. But at the end of the day, it happened because Allah destined it to happen. You were meant to get into a car accident at the time that you did because it was already written for it to happen. This is the Qadr of Allah.
Another example would be the one from the ayat above. "If this person would've stayed with us instead of engaging in the battle, they would not have died or been killed." Allah destined this person's life to end at the time that it ended. No questions asked. When we question the "what-ifs" in our lives, it's like questioning our faith in Allah (SWT). The Almighty is the one who gives life and causes death. He is the one who knows what and when things will happen whether it's a good or bad outcome.
May Allah guide us and keep us from questioning His Qadr.
This is a reminder to me first and then you. <3