This refers to the joining of the spirit with the body again, to bring it back to life. The Qurʾān has defined death as the departure of the spirit from the body. On judgment day, the spirit will re-enter the body again, and hence, the human being will come to life.
Secondly, this can also refer to the groups of people on judgment day because the Qurʾān has used the same word for the three groups on judgment day.49 There will be three groups, the righteous that will be on the right, the wicked on the left, and the foremost even among the righteous, that will be at the front.
When the Nufus are joined together
This refers to the joining of the spirit with the body again, to bring it back to life. The Qurʾān has defined death as the departure of the spirit from the body. On judgment day, the spirit will re-enter the body again, and hence, the human being will come to life.
Secondly, this can also refer to the groups of people on judgment day because the Qurʾān has used the same word for the three groups on judgment day.49 There will be three groups, the righteous that will be on the right, the wicked on the left, and the foremost even among the righteous, that will be at the front.
49 Q. 56:7