Trisagion

Gurdjieff
"You know the prayer 'Holy God, Holy the Firm, Holy the Immortal'? This prayer comes from ancient knowledge. Holy God means the Absolute or All. Holy the Firm also means the Absolute or Nothing. Holy the Immortal signifies that which is between them, that is, the six notes of the ray of creation, with organic life. All three taken together make one. This is the coexistent and indivisible Trinity.

three holy forces of the Sacred-Triamazikamno and then named them:

the first, ‘God-the-Father’;
the second ‘God-the-Son’; and
the third, ‘God-the-Holy-Ghost’;

and in various cases expressed the hidden meaning of them and also their longing to have a beneficent effect from them for their own individuality, by the following prayers:

‘Sources of Divine
Rejoicings, revolts and sufferings,
Direct your actions upon us.’
…

or Holy-Affirming,
Holy-Denying,
Holy-Reconciling,
Transubstantiate in me
For my Being.’
…

or ‘Holy God,
Holy Firm,
Holy Immortal,
Have mercy on us.’

The Greek phrase Trisagion translates as "Thrice Holy" – as in this hymn God is described as holy in three different qualities; Agios o Theos means "Holy God".

The hymn is of great antiquity, and perhaps much older than the event assigned by the Greek Menology as connected to its origin. The tradition recounts that during the reign of Theodosius II (408-450) Constantinople was shaken by a violent earthquake, 24 September, and that whilst the people, the emperor and the Patriarch Proclus of Constantinople (434-446) were praying for heavenly assistance, a child was suddenly lifted into midair, to whom all cried out Kyrie eleison ('Lord, have mercy'). The child was then seen to descend again to the earth, and in a loud voice he exhorted the people to pray : 'Holy God, Holy Mighty, Holy Immortal'. After giving this exhortation, the child died.

In English - Literal Translation:

Holy God, Holy Strong, Holy Immortal, have mercy on us.

In Latin:

Sanctus Deus, Sanctus Fortis, Sanctus Immortalis, miserere nobis.

fortis
(physically) strong, powerful
(figuratively), firm, resolute, steadfast, stout
(figuratively), courageous, brave

miserere nobis. 
Have mercy on us.

Trisagion - Wikipedia