St. Isidore, St. Francis de Sales and the Angels
St. Isidore was a farmer who lived and worked as a laborer in the fields near Madrid. He was accustomed before going to work to hear daily Mass. Some meddlesome people complained to the gentleman by whom he was employed that he gave his time to prayer and neglected his work.
His employer however, had no reason to complain, as Isidore's work was well done. Nevertheless, he went to see for himself and saw from a distance the yoke of oxen ploughing the land, led by a man whom he thought to be Isidore.
On approaching nearer, he saw that not a man but an Angel guided the oxen. It was Isidore's Guardian Angel who took his place.
Saint Frances de Sales converted immense numbers of the most hardened sinners. Before beginning his sermons, he would pause and look round on his listeners for some minutes.
Asked by some of his priests why he did so, he replied that he was addressing himself to the Guardian Angels of those present and begging them to take his words straight to the hearts of their clients. This custom enabled the Saint to convert thousands of misguided and wicked heretics.
It is a custom that we all should put in practice of praying to the Guardian Angels of our enemies and those hostile to us, to prevent them from doing us injury, and to the Guardian Angels of our friends to help them and keep them from all evil.
Source: Father Paul O'Sullivan, All about the Angels.