Thomas Aquinas, Compendium of Theology

He who looks on himself as a son of God, ought, among other things, to imitate our Lord especially in His love, as we are urged to do in Ephesians 5:1 f.: "Be ye therefore followers of God as most dear children, and walk in love." God's love is not restricted to any individual, but embraces all in common; for God loves "all things that are," as is said in Wisdom 11:25. Most of all He loves men, according to Deuteronomy 33:3: "He hath loved the people." Consequently, in Cyprian's words, "our prayer is public and is offered for all; and when we pray, we do not pray for one person alone, but for the whole people, because we are all together one people." Or, as Chrysostom says, "Necessity forces us to pray for ourselves, but fraternal charity impels us to pray for others." This is why we say, "Our Father," and not simply "My Father."

At the same time we should remember that, although our hope rests chiefly on God's help, we can aid one another to obtain more easily what we ask for. St. Paul says, in II Corinthians 1:10 f.: God will "deliver us, you helping withal in prayer for us." And in James 5:16 we are exhorted: "Pray one for another, that you may be saved." For, as Ambrose reminds us, "many insignificant people, when they are gathered together and are of one mind, become powerful, and the prayers of many cannot but be heard." This agrees with Matthew 18:19: "If two of you shall consent upon earth concerning anything whatsoever they shall ask, it shall be done to them by My Father who is in heaven." Therefore we do not pour forth our prayers as individuals, but with unanimous accord we cry out, "Our Father."

Let us also reflect that our hope reaches up to God through Christ, according to Romans 5:1 f.: "Being justified therefore by faith, let us have peace with God, through our Lord Jesus Christ, by whom also we have access through faith into this grace wherein we stand, and glory in the hope of the glory of the sons of God." Through Him who is the only-begotten Son of God by nature, we are made adopted sons: "God sent His Son . . . that we might receive the adoption of sons," as is said in Galatians 4:4 f. Hence, in acknowledging that God is our Father, we should do so in such a way that the prerogative of the Only-begotten is not disparaged. In this connection Augustine admonishes us: "Do not make any exclusive claims for yourself. In a special sense, God is the Father of Christ alone, and is the Father of all the rest of us in common. For the Father begot Him alone, but created us." This, then, is why we say: "Our Father."