Ḥijāb is an obstacle that comes between the thing desired and aimed for, and the one who desires and aims for it. Sari Saqatī used to say: O Allah! If You are to punish me with anything, do not punish me with the abasement of ḥijāb. (Lumaʿ, 428)
There are two kinds of ḥijāb: ḥijāb al-rayn (from which we seek refuge in Allah) is never lifted. (And then) there is also ḥijāb al-ghayn. This is lifted so quickly! The following saying is to clarify this: The essence (dhāt) of a servant becomes a ḥijāb to the Real (al-Ḥaqq). So much so that for him, truth (ḥaqq) and bāṭil (falsehood) are at the same level. For another servant, his attribute (ṣifa) becomes a veil between him and the Real, but his nature and heart (qalb) always seek the Real and flee from falsehood.
The essential ḥijāb is rayn; it is never lifted. Rayn (rust), khatm (seal), and ṭabʿ (stamp) have the same meaning. As Allah has said: "No! Rather, the stain [rayn] has covered their hearts for what they were earning." (al-Muṭaffifīn 83:14). Its ruling is even clearer in the following verse: "It is the same for them whether you warn them or do not warn them—they will not believe." (al-Baqara 2:6). Then He explained the reason by saying: "Allah has set a seal upon their hearts and upon their hearing." (al-Baqara 2:7). He also said: "Allah has set a seal upon their hearts." (al-Naḥl 16:108).
ḥijāb al-ʿizzah (the veil of majesty), which is the veil of attributes (ṣifa), can be lifted either at a specific time or at any time. The transformation of the essence (dhāt) is, in terms of ruling, strange and wondrous, and in terms of ghayn, impossible. The transformation of the attribute (ṣifa), however, is possible. (Hujwīrī, 7-8)
The world (dunyā) is a ḥijāb to the hereafter (ākhira), and the hereafter is a ḥijāb to the world and to the Lord of the hereafter. Whatever you are occupied with (or whatever your mind is attached to), that becomes a ḥijāb for you. Do not pay attention to people. Thus, you come to the door of the Real with the foot of the heart (qalb). The firmness of your renunciation (zuhd) from everything other than Him brings you to Him in a state (ḥāl) stripped of everything, bewildered (ḥayra) concerning Him, seeking refuge in Him, asking His help, looking to His precedence and knowledge. (Fath, 75)
Ḥijāb is anything that veils your eyes from what you seek. (Iṣṭilāḥ, 538)
Ḥijāb is the traces left by created forms (kawnī ṣuwar) that prevent the manifestations (tajallīyāt) of the Real (al-Ḥaqq) in the heart (qalb). (Jāmiʿ, 81)
ḥijāb al-ʿizzah (the veil of majesty) is the veil or curtain of majesty; it is amā (the cloud of unknowing) and bewilderment (ḥayra). (Iṣṭilāḥ, 540)