Gayatri Japa means – Let my intellect be inspired by the Divine.
It is our intellect which blocks the vast Divinity from expressing itself fully in life.
So, the prayer is, ‘May the Divine inspire my intellect. May the Supreme Energy manifest in my life and in my intellect.’
And in Upanayanam, they usually put a thread on you and the thread is to signify that you have a responsibility towards the knowledge, towards your parents and towards society. So it signifies carrying your responsibilities on the shoulders.
A young boy, before he goes to study, they make him realize that, 'You have the responsibility.’ And then the child studies and comes back.
When you have finished all your responsibilities, in Sanyasa, then they remove the thread and throw it.
If you are a recluse, then you don’t have the thread. This is a system that has been followed from a long time.