A Christian is defined not as someone who observes God's commandments and adheres to religious norms and practices, although it may entail that. That is a vague description because other religions do the same. Instead, a Christian is someone who has a healthy relationship with Christ.
What does it mean to have a healthy relationship with Christ? Imagine you have a good friend to whom you can just blurt out with abandon whatever is in your heart without fear of being judged. Imagine that you reciprocate by also listening intently when this friend has something to say to you. You spend time with each other often whether it playing golf, eating out, or just simply having a conversation over coffee. That is the kind of relationship we want with Christ. But such a relationship doesn't happen on its own. It needs to be cultivated through three ways.
A good friend cannot know us completely if we are not honest. So it is only to a close friend we confide the most shameful things we’ve done, or crack the most revolting jokes, or reveal our most personal secrets. It is only to an intimate friend we go for help for the most embarrassing request. Only by completely exposing ourselves slowly will we feel at ease with our friend in the long run. No deep friendship is made by small-talk; that will always end up as an acquaintance instead of a friendship.
Opening up is not easy to someone new at first because we always fear being ridiculed. We always fear that the cogs in our friend’s head are spinning some sort of judgment on what we divulge. However, we can’t get to a level of friendship if we don't risk it. Someone worth being a friend will accept you for who you are. They may not necessarily condone what you’ve done, but they will certainly accept you.
Trust ensues when after you tell your friend something personal and your friend repays the favor by revealing something personal in return. By telling each other something that came from your hearts, you've made a bond. However, this can't ever happen if you are the only one doing the talking. You must keep quiet at some point and give your friend a chance to talk. If you do all the talking, the encounter with your friend will not be a dialogue but a speech – and that certainly is one-sided as you would not have learned anything new about your friend.
We've all had this close friend in elementary school with whom we spent so much time in laughter, tears, eating, playing, and getting caught by the principal for doing mischievous things. You thought you would be friends forever, but as the years went by, you lost touch, and now he or she is but a dim memory. This happened because you did not get together more often. No judgment there, it's just the sad truth about every relationship that fades away.
There is such a stark contrast between friends that meet often and those that meet once a year. It is the frequency in meeting with the people that fan the flames of our friendship with them. By "living" with your friend, you begin to know your friend in a more intimate way. You just don’t know ABOUT your friend – as if it were information you get from Facebook, Linked In, or Instagram – but you actually get to KNOW your friend. There is a big difference.
So how does prayer fit into this? Mental Prayer is the way to accomplish all three: honest talking, intent listening, and frequent encounter. We need to be able to tell Christ what it is we feel deep in our hearts. We must be able to listen to what he says to us too. And we must spend frequent time with him. The Catechism tells us that we must live with a vital relationship with the living and true God – and that relationship is prayer (CCC §2558).
There are three forms of prayer: vocal, mental, and contemplation.
Vocal prayer is when we use words to communicate to God. The Our Father is a vocal prayer, for example, so is the spontaneous or formulated prayers we say when we bless our food before meals.
Mental prayer is when we use our minds to try and understand what God is trying to tell us. We usually use scripture, or an image, or a song – or even looking at a beautiful sunset – as a catalyst. While vocal prayer is communication directed to God, in Mental Prayer we seek what God is trying to communicate to us.
Contemplative prayer is when God’s lifts up and wraps a person in an intimate "hug" with him. Usually no words are used; instead, you are allowed to bask in his divine light. Sometimes one experiences extreme joy being in the presence of God, while sometimes there is no feeling at all. We cannot create it. We cannot control its length. It is a gift. Vocal and Mental prayer usually paves way to contemplation.
It would be difficult to rank which of the three is best because prayer is prayer regardless of the form. However, it can be said that Mental Prayer is the one that normally develops a relationship with Christ, because we speak to him, listen to him, and spend time with. If a Christian is someone who has an intimate relationship with Christ, we can see why prayer is important for it develops that relationship. It is a valuable tool we can't ignore.