There is a story about Lord Kartikeya from the Puranas.
When Kartikeya was a young child, His father, Lord Shiva asked him to go and study and receive education from Lord Brahma. So Kartikeya went to Lord Brahma and asked him, ‘Please tell me the meaning of Om.’ Lord Brahma said, ‘First learn the alphabets! You are directly asking for the meaning of Om.’ Kartikeya said, ‘No, I want to know the highest knowledge first – Om.’
Now Lord Brahma knew all about the alphabets, but he did not know the meaning of Om (the primordial sound). So Kartikeya said to Lord Brahma, ‘You do not know the meaning of Om, how will you teach me? I will not study under you.’ And Kartikeya went back to his father, Lord Shiva.
Lord Brahma told Lord Shiva, ‘You alone can handle your son. I can’t handle him. If I say this, he says that. Whatever I say, he says the exact opposite of that. I won’t be able to teach him. So you decide what is best and handle him.’ Hearing this, Lord Shiva asked Kartikeya, ‘What happened son? Lord Brahma is the Creator of the entire universe. You must learn from him.’
To this Kartikeya replied, ‘Then you tell me, what is the meaning of Om?’
Hearing this, Lord Shiva smiled and said, ‘Even I don’t know.’
Kartikeya then said, ‘Then I will tell you because I know the meaning of Om.’
‘Then tell me the meaning since you know it’, said Lord Shiva. ‘I can’t tell you like this. You have to give me the place of the Guru. Only if you put me on the pedestal of the Guru can I tell you’, said Kartikeya.
Guru means he has to be on a higher position or platform. The teacher has to sit on a higher place and the student has to sit down and listen to him.
How can Lord Shiva find a seat higher than Him, for He is the highest and greatest of Gods? So then Lord Shiva lifted the young Kartikeya on to His shoulders. And then in the ear of Lord Shiva, Lord Kartikeya explained the meaning of the Pranava Mantra(Om).
Kartikeya explained that the entire Creation is contained in Om.
The Trinity – Lord Brahma, Vishnu and Shiva are contained in Om.
Om means that everything is love – unbroken and unshakeable love is Om. This is the essence and also the secret of Om that Lord Kartikeya narrated to Lord Shiva.
Upon hearing this, Goddess Parvati (Mother of Lord Kartikeya, and an incarnation of the Mother Divine) was elated and overcome with joy. She said, ‘You have become a Guru (Swami) to my Lord (Natha)!’ Saying this she addressed her son as Swaminatha, and ever since Lord Kartikeya also came to be known as Swaminatha.
So in this way, Lord Kartikeya assumed the position of the Guru and explained the meaning of Om to Lord Shiva by sitting on his shoulder. So the essence of the story is this –