Firstly: The Definition of Ihram
Linguistically, ihram means entering into a state of prohibition. One says “a man entered into ihram” when he enters into the prohibition of a treaty or covenant. Thus, what used to be permissible for him is now prohibited.
Technically, ihram is the intention of commencing rites.  Ibn `Uthaymin says: “Whoever wears the garments of ihram without an intention has not entered into ihram. On the other hand, whoever intends rites has entered into ihram even if he does not wear the garments of ihram. However, he has transgressed one of its restrictions.” This is the position of the majority: the Malikis, Shafi`is, and Hanbalis.
Secondly: Wisdoms behind Ihram being Legislated
Some of the wisdoms behind ihram being legislated include:
1. Embodying slavehood to Allah, exalting Him, and obeying His command.
2. Manifesting equality amongst all Muslims: rulers and subjects, rich and poor.
3. It is a reminder of the Last Day and resurrection.
Thirdly: The Ruling of Ihram
Ihram is one of the fard acts concerning rites, whether Hajj or `umrah. Consensus on this was related by Ibn Hazm.