Imām Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. They were deceiving the believers, so it is as if they sought to deceive Allāh. [Ibn ʿAbbās, Ibn Qutaybah]
2. They sought to deceive the Prophet of Allah (ﷺ), so Allāh spoke of the Prophet (ﷺ) in the position of his Lord, just like He said, "Indeed, those who pledge allegiance to you (O Muḥammad), they are actually pledging allegiance to Allāh" (48:10). [Al-Zajjāj]
3. "*Khādiʿ*" in the Arabic language means corrupt, so the verse means that they spoil the faith which they display outwardly with their hidden disbelief. [Ibn al-Anbārī]
4. Their behavior towards Allāh's religion would be called "deception" if they treated each other that way.
5. They used to hide their disbelief while making an outward show of faith.

Imām Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. They will suffer the consequences in this worldly life, in one of two ways:
(i) They are lured further in and given more time, so their punishment is increased.
(ii) By the Prophet (ﷺ) and the believers being made aware of their hidden realities.

2. They will suffer the consequences in the Hereafter. There are two interpretations about this:
(i) It will be when the barrier is placed between them and the believers, as mentioned in the verse: "It will be said, 'Go back behind you and seek light.' And a wall will be placed between them with a door" (57:13).
(ii) When they see (and are looked upon by) the people of Paradise, they desire to have some of the comfort that the believers have. They will say: "Pour upon us water or whatever Allah has provided you." The believers will respond to them: "Indeed, Allah has forbidden them both to the disbelievers" (7:50-51).

In what sense are the hypocrites only harming themselves?

Imām Ibn al-Jawzī (d. 597 AH / 1201 CE) said in his book "Zād al-Masīr":

1. Allāh informing His Prophet (ﷺ) about their lies. [Ibn ʿAbbās]
2. The harms of their disbelief upon their own selves. [Ibn Zayd]