First, He is not an animal. Everything originally was created by God, and thus we have this transcendental Lion form. But that may not be enough for some, which is fine. So here's more:
Understand, God is unlimited. Many say or think: "Well, yes, of course God is unlimited." If we believe that, we need to accept He can appear however He darn well pleases. :) But why a lion, or half lion/half man? Details on that will be clarified below. First....
I am trying to have compassion & understanding that this form as God is difficult to fit into the brain. It can be hard or at least a bit unclear, to some, why God would choose to appear in these various ways.
Over time & with explanation, anyone can comprehend it. Maybe God is having fun. After all, these are pastimes. Maybe He is protecting his devotee. Devotees don't like to say "maybe" as it's often viewed as speculation. I was just having fun, not speculating as you will see below. Anyhow, there are many reasons we may not initially have thought up, He did. :)
However, I'd like to add a point I do not feel I have brought up before, at least not here.
Looking at various religions, we see similar belief in the unusual. For example, from the Bible we have a person who turned to salt, Noah's Arc, a burning bush, and much more. All of which many believe deeply.
Kindly do not assume I don't or do believe in these. I have not disclosed that here. It would take a huge post to explain my point of view on those. Simply pointing out - if one can believe the Biblical "Jonah and the Whale," please make room for Nrsimhadeva.
Next, a young 5 year old boy [named Prahlada] was being severely, SEVERELY, abused by his father. Actually, his father tried to murder him, repeatedly.
HaranYaKashiPu (the dad), was a very powerful king. Yet he increased that strength by preforming austerities reputed to grant mystical power too.
As a reward for such austerities, he asked to be blessed to never ever die. Lord Brahama [a demi-god, not to be confused with God], told him he could not grant such a blessing.
This clever father [HaranYaKashiPu] said fine, then benedict me that I shall never be killed in daytime nor night. Not inside nor outside. Not by any weapon, not by any man nor by any animal. ....You get the picture. :)
Brahama said ok. To make a long story short, when Lord Nrsimha [God] appeared, He made sure not to break any of those promises.
Haranyakashipu was not killed in the day nor the night, but at twilight. He did not die inside nor outside, but in between the two, on a threshold on the Lords lap. He also did not die by any weapon but by the Lords transcendental nails. He was not killed by any man and not by any beast - but by a half man/half lion transcendental incarnation of Krishna known as Lord Nrsimhadeva.
In order to protect little child Prahlada, who also was a devotee, Lord Narasimha appeared in this way to still observe the promises, yet to make the abuse and chronic attempts at murder - stop.
Some may wonder, "Why didn't God just zap Haranyakashipu with mercy, healing, etc?"
The answer is long and I'm trying to keep this post short. Simply put: In his past life Haranyakashipu was a devotee but made a big offense. Karmic reaction / consequences presented them-self. Yet a type of mercy was given. He was offered a choice. Did he want to take many births as a devotee, or shorten all those births as demon?
Haranyakashipu himself made the choice to take birth as a demon and be killed by God. When one is killed by God, he or she is immediately liberated!
The other day was Lord NarasimhaDeva's Appearance day and on fb I often wonder how my nondevotee pious friends handle this. I become a tiny bit concerned posting about Him, for their sake of course. I will always post about God, but wish to do so with explanations when needed. Thus this blog post. Hope I've cleared up any confusion about this wonderful incarnation, because He is here to protect you!
Scripture: "When Lord Nṛsiṁhadeva appeared, Prahlāda Mahārāja was never afraid of Him, whereas his atheist father was immediately faced with death personified and was killed. Therefore, although Lord Nṛsiṁhadeva appears as death for an atheist like Hiraṇyakaśipu, He is always kind and is the reservoir of all pleasure for the devotees like Prahlāda. A pure devotee is not, therefore, afraid of birth, death, old age and disease." Source: Srimad Bhagavatam 10th Canto, also known as Kṛṣṇa Book, Chapter 87
"In the Nṛsiṁha Purāṇa, Lord Nṛsiṁhadeva says: 'Anyone who prays unto Me and takes shelter from Me becomes My ward, and I protect him always from all sorts of calamities." Source: Nectar of Devotion, Chapter 11
Full "Nectar Of Devotion" / free book, opens here.