The phrase mā-bayna aydīhim wa mā-khalfa-hum is interpreted in four ways:
1. The expression mā-bayna aydīhim refers to what existed before their creation; and mā-khalfa-hum is used in the sense of what came after their creation, as in the following verses:
He knows mā-bayna aydīhim (that is, what existed before them—the angels—before their creation) and mā-khalfa-hum (that is, what came after them/the angels after their creation). (al-Baqara 2:255)
Mā-bayna aydīnā (that is, what existed before our creation) and mā-khalfana (that is, what came after our creation)... (Maryam 19:64)
He knows mā-bayna aydīhim (that is, what existed before them/the angels) and mā-khalfa-hum (that is, what came after them/the angels). (Ṭā-Hā 20:110)
2. Bayna aydīhim is used for the Hereafter, and khalfa-hum for the world; as in the following verses expressed through the words of Gabriel:
Mā-bayna aydīnā (that is, everything in the Hereafter) and mā-khalfana (that is, everything in the world) belong to Him. (Maryam 19:64)
Then I will approach them; min-bayni aydīhim (that is, coming from the direction of the Hereafter, I will inform them that there is never any resurrection after death) and min-khalfīhim (that is, coming from the direction of the world, I will make it seem pleasing to their eyes). (al-Aʿrāf 7:17)
We set devils upon them. They made mā-bayna aydīhim (that is, the idea that there is never any resurrection in the Hereafter after death) and mā-khalfa-hum (that is, the world: they made it seem pleasing to their eyes) attractive to them. (Fuṣṣilat 41:25)
When it is said to them: "Ittiqū mā-bayna aydīkum (that is, against the punishment of the Hereafter) and mā-khalfakum (that is, against the punishment of the world)..." (Yā Sīn 36:45)
3. The phrase mā-bayna aydīhim wa mā-khalfa-hum expresses precedence and succession in the world; as in the following verses:
Min-bayni yadayhi (that is, before him, messengers such as Hūd and Ṣāliḥ had been sent to their peoples) and min-khalfihi (that is, after him, warners who said "Do not worship anyone but Allah!" came and went). (al-Aḥqāf 46:21)
When their messengers came to them, min-bayna aydīhim (that is, from among them; the messengers who came before Hūd and Ṣāliḥ to their peoples) said, "Do not worship anyone but Allah..." (Fuṣṣilat 41:14)
4. With the phrase mā-bayna aydīhim wa mā-khalfa-hum, relatives and tribe are intended; as in the following verses:
Do they not see from the heaven and the earth, mā-bayna aydīhim (that is, those before them) and mā-khalfa-hum (that is, those behind them)? (Sabaʾ 34:9)
For the son of Adam saw the heaven and the earth both before him and behind him.
We placed a barrier min-bayni aydīhim (that is, in front of them) and a barrier min-khalfīhim (that is, behind them). (Yā Sīn 36:9)