You might have this doubt.
Why do we have so many different mantras for the same Devata?
For example for Ganesh Ji
Ekakshara mantra - गं is there.
गं गणपतये नमः is there which is called the Ashtakshara mantra.
ॐ गं क्षिप्रप्रसादनाय नमः - the Kshipraganapathy mantra is there.
All are Ganesha mantras.
But devata is the same, then why so many different mantras?

During Vanavasa, Sriram Ji visited Bharadwaja Ashrama.
Maharshi welcomed him, offered him fruits and water, a place to rest.

While returning from Lanka with his retinue in Pushpaka Vimana, he again halted at Bharadwaja ashrama.
The ashrama was decorated to receive a VIP.
There were musical instruments - drums and trumpets.
Sumptuous delicacies were served in golden plates.

Sriram Ji asked Maharshi.
What is this?
Last time I came here, you received me in such a simple manner.
Now all this pomp and glory!
Has your ashrama prospered so much?

Maharshi said-
It's not about the prosperity of my ashrama.
अवस्था पूज्यते राम ! शरीरो न तु पूज्यते ।
Rama ! It is not your body that is worshiped, it is your state.

Last time when you came here, you came here as an ascetic, wearing clothes befitting a tapaswi.
I treated you accordingly.
Now, you have come as a king.
I have to treat you like a king.

Devatas have got different bhavas or avasthas.
You van see Lord Shiva as a family man with Parvathy Devi, Ganesha, and Krtikeya.
You can see him as Jagat Guru, Dakshinamurthy.
You can see him in the dancing form, Nataraja.
Each one is a different avastha of the Lord.
Each avastha or state has a different mantra.

Let's say you have a Police inspector as your neighbor.
You visit his home for his son's birthday party.
You will have certain expectations from him.
But if you are visiting him in the police station to file a complaint, then what you expect from him is different.
The way he treats you will also be different.
What he can give you at home as a host and what he can give at the police station as an Inspector are completely different.
They are two different states of the same person.

In the same way, Devatas have got different avasthas and mantra for each avastha.
This can be understood from the dhyana shloka associated with each mantra.
What a devata can give you in his or her different avasthas are also different.

You can worship Krishna for protection, for success, for knowledge, for moksha.
The mantra for each purpose will also be different.