You don't have to be Catholic or even a Christian to share the beauty and truth of the prayer of St. Francis. You just have to be a good person. You can leave out the "Divine Master" and the "Amen" and still benefit fully from the message. As for the "eternal life", we can hope, even if we doubt.
Lord, make me an instrument of your peace.
Where there is hatred, let me sow love;
where there is injury, pardon;
where there is doubt, faith;
where there is despair, hope;
where there is darkness, light;
and where there is sadness, joy.
O Divine Master,Grant that I may not so much seek
to be consoled as to console;
to be understood as to understand;
to be loved as to love.
For it is in giving that we receive;
it is in pardoning that we are pardoned;
and it is in dying that we are born to eternal life.Amen