Al-Ghadab, linguistically means anger, it is the opposite of pleasure (rida) and one of the Attributes of Allah. (al-Alusi) Maghdub refer to the objects of anger.
Dalal linguistically means to divert from the intended goal or to diverge from the true path and it is the opposite of guidance. Its essential meaning is disintegration and dissolution (Abu Hayyan), as such it is said, ‘the milk dalla in the water’ when it is mixed such that it disappears. In this respect also is His saying, “And they say: when we become tall in the earth are we then to be in a new creation?” (as-Sajdah 32:10) Meaning when we die and disappear into the earth by becoming dust. Ad-Dallin refers to those gone astray. (ash-Shawkani)
Who does this verse refer to? At-Tirmdihi records on the authority of Aid bin Hatim who said, “I asked the Messenger of Allah, peace and blessings of Allah be upon him, about, “Those who have earned [Your] anger”, and He said, “It refers to the Jews.” I then asked about, “those who have gone astray” and he said, “The Christians are those who have gone astray.” (At-Tirmidhi 2953)
The Jews and Christians, even though both of them are misguided and both of them have Allah’s anger on them, the anger is specified to the Jews because the Jews knew the truth, rejected it and deliberately came with falsehood. Therefore the anger of Allah being upon them was the description most befitting them. The Christians were ignorant, not knowing the truth, so misguidance was the description must befitting them.
This is further proven by the sayings of Allah concerning the Jews, “So they have drawn on themselves anger upon anger” (al-Baqarah 2:90) “Say: shall I inform you of something worse than that, regarding the recompense from Allah; those (Jews) who incurred the curse of Allah and His anger.” (al-Maidah 5:60) “Indeed those who took calf (for worship), anger from their Lord and humiliation will come upon them” (al-Araf 7:152) and Allah said concerning the Christians, “And do not follow the vain desires of people (i.e. the Christian) who went astray in times gone by, and misled many, and have themselves strayed from the Straight Path.” (al-Maidah 5:77)
Other opinions have been voiced concerning the meaning of this verse, (ibn al-Qayyim) but the meaning mentioned above takes precedence and is undoubtedly correct as it has been reported from the Prophet, peace and blessings be upon him, himself. (Abu Hayyan)
The Spiritual Cure: An Explanation of Surah Al-Fatihah prepared and translated by Abu Rumaysah Pages 169-172