Sincere faith gives us personal peace.

The Talmud tells us to have faith/emunah by attributing to God all that happens to us:

“…For good news, one says: ‘Blessed be He that is good and does good.’
For bad news, one says: ‘Blessed be the True Judge’.” [1]

But it goes even further, indicating that when we have progressed enough spiritually, even the “bad” will be seen as “good” :

“Rabbi Aha b. Hanina said:
‘Not like this world is the world-to-come.
In this world, for good news one says: ‘…He is good and does good’,
while for bad news, he says: ”Blessed be the True Judge.’
In the world-to-come, it shall be only: ‘He is good and does good’.” [2]

Rebbe Nachman confirms that the real goal is to achieve this during our lives here:

(Rebbe Nachman of Breslav said):
“When a person knows that everything that happens in his life is for the good, it’s like a glimpse of the world-to-come.” [3]

The essence of faith/emunah, then, is to thank God for all that happens and accept it as being for the good.

I happened to read about a Christian hymn, “It Is Well With My Soul,” that exemplified the same spiritual truth. The author, Horatio Spafford, was a 19th century American businessman who underwent a series of awful tragedies. Yet, his response was to write a hymn affirming that through faith that all is in God’s hands for the good, he was able to face it all with peace in his heart and soul. [4] [5]

These confirm, too, what Rabbi Bachya ibn Pekudah said a thousand years ago:

“Among the worldly advantages of trust in God are to be counted: a heart at rest, without worldly cares; a tranquil spirit, liberated from mental disturbance and free from the pain of the lack of physical enjoyments.” [6]

and

“A further advantage is that he rejoices, whatever the situation in which he’s placed, even if it is contrary to his nature, because he always trusts that God won’t do anything but what is for his good in all things, just as a tender mother acts towards her infant child — bathing it, diapering it… — all without regard to the infant’s will, as David, peace on him, said, ‘I have stilled and quieted my soul like a weaned child with his mother… (Ps. 131:2)’.” [7]

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[1] Brachot 54a (Mishnah 9:1)
[2] Pesachim 50a
[3] Likutei Moharan, lesson 4
[4] for the full story and the original lyrics:
https://en.wikipedia.org/wiki/Horatio_Spafford
[5] For a performance of this hymn, with slightly revised lyrics:
https://www.youtube.com/watch?v=nCg-QXhhC5I
[6] Bachya; Duties of the Heart; Feldheim, vol. 1, p. 291
[7] ibid., p. 293