Niels Hemmingsen, in the Enchiridion theologicum‘s locus on prayer, takes the address of the Lord’s Prayer, “Our Father,” as referring not to the Person of the Father, but to the divine nature or the Triune God. 1 This is because he sees prayer as directed to the Godhead as such.
Here is what he says:
First, then, this beginning [of the Lord’s Prayer] teaches us who is to be invoked, namely GOD, whom we are commanded to address by the name “Father.” For it is not permitted to address any other than him whom the Lord commands us to invoke. However, we should observe that FATHER in this places is not the name of one Person, but of the essence. For every invocation that is made to God is understood to embrace the Father, the Son, and the Holy Spirit. Next, the Son is to be invoked in a double way, first together with the Father and the Holy Spirit, as God, the giver of all good things, next as the mediator who has been sent and who intercedes. 2
Gregory of Nyssa, in his second discourse on the Lord’s Prayer, is getting at the same thing, I think, though he does not use Trinitarian language in doing so:
On the principle then that the vow has been fulfilled, the Lord said to the disciples: “When you pray, say, ‘Our Father who art in heaven’” (Mt 6:9). Somewhere in the Psalms the great David says, “Who will give me wings like a dove” (Ps 55:6)? I, too, would dare speak with the same voice. Who will give me such wings as to fly with my mind to the height of the noble meaning of these words? I need to leave the whole earth behind. I must traverse all the intermediary air and come to that ethereal beauty, reaching the stars and beholding their lovely order.
Even then I could not remain with the stars. I would need to pass through them and go beyond all material things that change and are in flux. I would want to reach the eternal nature of God, the unshakable power, which has established itself and governs the universe. All things exist and are dependent on the ineffable will of the Divine Wisdom. I would have to remove my mind far from all things that change and are in flux. By attaining to an unchanging and unwavering disposition of the soul, I would first earnestly make Him my friend who is eternal and unchangeable. Only then would I invoke that most intimate Name and say, “Father!”
What quality of soul must the speaker possess to speak of God as “Our Father!” What confidence of spirit! What purity of conscience! To perceive God’s ineffable glory, he must comprehend the mystery of God as far as it is possible from the names that have been conceived of and attributed to God in the Scriptures. He must learn that the divine nature of God is goodness, holiness, joy, power, glory, purity and eternity. Whatever God may be in His deep mystery, He possesses all these eternal and many other conceivable attributes that properly belong to the Divine Nature. Let us say that a person could understand all these endowments of God through the study of Holy Scriptures as well as one’s own creative reflection. Could such a person even then dare to utter the sacred Name and call such a God his own Father?
One thing is very clear. If he had any sense, he Would not dare address God with such a Name and say “Father,” unless he perceived a reflection of the same attributes in himself. For it is impossible that God who is good in His very essence should be the Father of anyone engaged in evil activities. God who is holy could not be the Father of one defiled in life, nor He who is Eternal be the Father of one prone to every change, nor He who is the Father of life be the Father of one dead in sin. Similarly, God who is pure and spotless cannot be the Father of those who behave unseemly, neither can God who is generous be the Father of those who are greedy, nor the All Good One be the Father of those who in any way participate in evil things. (Tr. T. G. Stylianopoulos)