Beautiful answers and here is a more detailed answer.
I guess you are aware of the background in which Maharshi Quotes(Wrote on a Paper)these words.
At the outset, when Bhagavan left home, his family tried to trace him,
but failed. Only some years later they discovered him at
Tiruvannamalai. The Mother, not yet ripe to renounce the world and
join him, went to persuade her son to return home. It was in December
of 1898. At this time Bhagavan was not speaking and sat in apparent
indifference to her pleas. One Pachaiappa Pillai who was nearby gave
Bhagavan a paper and pencil and asked him to at least write a few
words of consolation to his mother. He wrote briefly that whatever is
destined to happen will happen. - Ramana Maharshi Collected Works
If we understand the context, Maharshi's mother was under the assumption that Bhagavan's act of leaving Home is volitional.So she was pleading him to return home using the same volition.
Maharshi wrote these words to console her and as well as a spiritual instruction.
Maharshi instructs that the fate of Jivas(Individuals) are controlled by Ordainer(Saguna Brahman/God)according to their past actions. The fruits of our actions are dispatched in a way beneficial to our spiritual progress.
And our efforts to control the fruits(outcomes) of our actions by trying to prevent some events from happening and by trying to make some events to happen is futile.
The best action therefore is to understand this fact and simply abide in oneself(Be As You Are / Abide in One's True(Own) Nature) without proliferating our egocentric actions.
The quote resonates with following verses, one from Maharishi's Upadesa Saram and another from Bhagavad Gita.
Upadesa Saram Verse 1:
Action yields fruit,
For so the Lord ordains it.
How can action be the Lord?
It is insentient.
The lord dwells in the hearts of all beings O Arjuna, and by his Maya causes all beings to revolve as though mounted on a machine.