Some of the purpose of the spiritual night journey of Prophet Mohammed:
God - be glorified - shows to His prophets the spiritual world of the Afterlife or the Next Life.. so that the prophet will have certain belief and gain essential knowledge, and his perception and idea will be much different following such experience.
One of my friends said: Certainly Prophet Mohammed was different in opinion and conception following his "Isra and Mi'eraj" , i.e. his night journey from the Inviolable mosque in Mecca to the Aqsa mosque in Jerusalem, then his ascension to the ethereal heavens (or the kingdom of heavens.)
I add to this, that is understood from many ayat of the Quran:
Quran 17: 1, which means:
(
Glorified be [God] Who took His servant [Mohammed] in a journey by night from the Inviolable Mosque [at Mecca] to the Remote Mosque [: the Aqsa mosque at Jerusalem], the precinct of which We have blessed [with much trees and fruits], to show [Mohammed, some] of His signs [in the ether world.]
Surely [God] is the All-Hearing [of the prayer of His servant Mohammed a], the All-Seeing b.)
........................................................................................
1
a When he prayed God to show him the souls and angels.
1
b Of the advantages of His servant, so He answered his prayer.
More explanation:
http://quran-ayat.com/pret/17.htm#a17_1
quran-ayat.com/pret/17.htm#a17_1
Therefore, among the purpose of this journey was "
to show him [some] of His signs [in the ether world."
That is because the Prophet prayed God to show him the angels and the souls, and then God answered his prayer and let him go in this spiritual journey to acquaint him, and he certainly following this journey had much more knowledge about the Afterlife.