The Third Petition
19 Q. What do we ask in the Third Petition: Thy will be done on earth as it is in Heaven?
A. In the Third Petition: Thy will be done on earth as it is in Heaven, we beg the grace to do the will of God in all things by obeying His Commandments as promptly as the Angels and Saints obey Him in Heaven; and we also beg the grace to correspond to divine inspirations and to live resigned to the will of God should He send us tribulations.
20 Q. Is it necessary to do the will of God?
A. It is as necessary to do the will of God as it is to work out our salvation, because Jesus Christ has said that they alone who have done the will of His Father shall enter into the Kingdom of Heaven.
21 Q. In what way can we know the will of God?
A. We can know the will of God especially by means of the Church and of the spiritual superiors appointed by God to guide us along the way of salvation; we may also learn His most holy will from the divine inspirations that come to us and from the very surroundings in which the Lord has placed us.
22 Q. Should we always recognise the will of God in adversity as well as in prosperity?
A. Both in prosperity and adversity we should always recognise the will of God, who directs or permits all things for our good.
(Tomorrow, The Lord's Prayer - The Fourth Petition)
Pius X, Pope St.. Catholic Catechism of Saint Pius X (1908) (pp. 47-48). Kindle Edition.