Here are some words and inspiring passages you may want to include in your note of sympathy, accompanied by your personal message. If you'd like a message randomly (if you believe in random) generated for you, go here.

plant a seed that grows

Love, like the ocean,
is vast and forever,
And sorrow, but a shadow
that moves over the sea.
(John Gray)

Like a bird
Singing in the rain,
Let grateful memories
Survive in time of sorrow.
(Robert Louis Stevenson)

For life and death are one,
even as the river and the sea are one.
(Kahlil Gibran)

Let me not pray to be sheltered from dangers but to be fearless in facing them.
Let me not beg for the stilling of my pain but for the heart to conquer it.
(Rabindranath Tagore)

And ever has it been that love knows not
its own depth until the hour of separation.
(Kahlil Gibran)

And you would accept the seasons of your heart,
even as you have always accepted the seasons
that pass over your fields.
And you would watch with serenity
through the winters of your grief.
(Kahlil Gibran)

And could you keep your heart in wonder at the daily miracles in
your life, your pain would not seem less wondrous than your joy.
(Kahlil Gibran)

Death…is the name given to a change which comes when one leaves
the coarse atmosphere of the earth and enters a finer one of Light.
Something like the sun setting in one place and rising in another.
(Kirpal Singh)

Why do you mourn the loss of your parents? I shall tell you where
they are: they are only within ourselves and are ourselves. For the
life-current has passed through innumerable incarnations, births
and deaths, pleasures and pains…just as the water current in a river
flows over rocks, pits, sands, elevations, and depressions on its way, but
still the current is unaffected.
(Sri Ramana Maharshi)

Whatever comes will go. Whatever goes will come.
(Yogiraj Sri Swami Satchidananda)

Every one can master grief but he that has it.
(William Shakespeare—MUCH ADO ABOUT NOTHING, Act III, sc. 2)

Complete letters of condolence after which to model your own:
When you know the deceased;
When you didn't know the deceased.

Famous historic letters.