Saint Francis of Assisi gives us this mantra about the basis of zeal.
Breathing in: My God . . .
Breathing out: and my all.
A Prayer for Zeal
Implant within my heart, O God,
the fiery zeal of a Jeremiah,
the conviction of a Ruth or Rebecca
and the zest of a Francis of Assisi.
Stir my slumbering soul,
that it might sing a song of passion and devotion,
drunk with dancing joy and desire for you,
my divine and loving Friend.
May my heart be as hot as the heart of Moses
for all your children burdened by slavery,
for all who feel oppression's steely heel
or suffer rejection in an alien land.
May I, like your son Jesus,
be consumed with zeal for you, Divine Beloved,
for life, for justice and for peace;
for all that I know in faith.
Fill me with zeal, O God.
— Edward Hays in Prayers for a Planetary Pilgrim