An extract from the Navarre Bible Commentary on yesterday's mass reading:
"(Jesus told His disciples,)  "Ask, and it will be given you; seek, and you will find; knock, and it will be opened to you." -- Matthew 7:7-12
PRAYER IS a raising of mind and heart to God to adore Him, to praise Him, to thank Him and to ask Him for what we need ("St. Pius X Catechism"). Jesus emphasizes the need for petitionary prayer, which is the first spontaneous movement of a soul who recognizes God as his Creator and Father. As God's creature and child, each of us needs to ask Him humbly for everything.
In speaking of the effectiveness of prayer, Jesus does not put any restriction: "Every one who asks receives", because God is our Father. St Jerome comments: "It is written, to everyone who asks it will be given; so, if it is not given to you, it is not given to you because you do not ask; so, ask and you will receive" ("Comm. in Matth.").
However, even though prayer in itself is infallible, sometimes we do not obtain what we ask for. St. Augustine says that our prayer is not heard because we ask "aut mali, aut male, aut mala." "Mali" (= evil people): because we are evil, because our personal dispositions are not good; "male" (= badly): because we pray badly, without faith, not persevering, not humbly; "mala" (= bad things): because we ask for bad things, that is, things which are not good for us, things which can harm us ("De Civitate Dei, XX", "De Serm. Dom.In Monte"). In the last analysis, prayer is ineffective when it is not true prayer. Therefore, "Pray. In what human venture could you have greater guarantee of success?" ([St] J. Escriva, "The Way").