Our Blessed Mother Mary is emphasizing, all the time in Her messages in Medjugorje, that Satan is very powerful and very strong and that he wants to disturb us and stop us in everything that we are trying to do. That is why she is asking us to increase our prayers so that we will be able to keep Satan away by our prayers. In that way, Satan would be harmless. She said the best way to do that is with the Rosary in our hands. The best weapon against Satan is the Holy Rosary.
Catholic Bible 101
"MY CHILD, you need not know much in order to please Me; only love Me dearly. Speak to Me as you would talk to your mother, if she had taken you in her arms. Have you no one to recommend to Me? Tell Me the names of your relations, of your friends; after each name add what you wish Me to do for them. Ask a great deal: I love generous hearts that forget themselves for others." St Peter Eymard