It is right and good to ask God for all the things we truly need. It is perhaps less good to ask for the things we want, but so long as those things are the goods of the spiritual realm, it is still right and proper. It is of questionable worth to ask for things we do not need but merely want with no real notion of what we would do with them once we had them. But even this is worthwhile because it exposes us to our own depths. These are mere vocal prayers. And yet we are enjoined to ask for what we need each day and to turn to the Lord to supply those needs. From this prayer, properly said, a more exteneded conversation with the Lord can occur.
St. Teresa defined mental prayer,
Mental prayer in my opinion is nothing else than an intimate sharing between friends; it means taking time frequently to be alone with him who we know loves us (Life 8, 5).
Mental prayer is an intimate sharing between friends. Such a sharing is not really possible if we are keeping things back. If we have a person with whom we want to be friends, we find that the roadblocks to friendship can be many. But the greatest of these are things about ourselves that we do not want known. The more we keep back the harder it is to share with a friend because we always fear revealing something that would damage the relationship.
However, God knows all. There is nothing we could possibly keep back even if we wanted to. The important point is that while God knows all, He wants us to share it. Often there is great power and tremendous release in simply saying what we know to be true. That is in acknowledging our weaknesses, we open the door to further intimacy. Thus the practice of confession is both about getting our sins out in the open and opening the door to greater intimacy.
Back to the original point--praying for what we want. When we do this, however frivilous the thing we want, we are at least being honest and opening the conversation. Now, if we become obsessed with what we want and continue like a small child to insist upon it in ever detail. conversation may not continue. If however, we are really ready to talk and listen and we say what it is we want, then even those material desires become the ground for intimate conversation and ultimately for conversion. So long as we are not flippant and we are really speaking our heart's desire, we open the gate for the Lord to enter.
Mental prayer is that extended conversation that comes from well-said vocal prayer. If we pray with sincerity and with earnestness, allowing God to peer into us, we start the conversation. Once it has begun, it can continue throughout the day or throughout a lifetime.