Prayer is communication with God, through prayer - we praise God, we confess our short comings our inadequacies or sin to God, we give thanks to God, we ask God to work on our behalf. Through prayer we show that we are dependant on God.
I'm not sure what you mean by Christian service but if you want to serve God then you would want to serve God according to God's plan for you. Through prayer you can ask God to reveal to you where and how God wants you to serve HIm. Also, once in some form of service for God then you need to do that in God's strength not your own strength so continued prayer is necessary.
An Angelus is a Christian devotion in memory of the Incarnation, or the bell rung as a call to prayer during the Angelus service.
One Christian prayer that many religions use is found also in the Bible, it's the Our Father prayer.
No. That is a Christian prayer.
The prayer at the end of a Sikh service is called the Ardas.
A prayer service consists of Christians gathering in a selected location to spend time praying. Sometimes prayer service can be called to pray about a specific request in the church.
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The service of morning prayer traditionally recited at daybreak is part of the Divine Office and is specifically called Matins - it is known as "the praising of God at the rising of the Sun".
An invocation is a call to prayer that opens a particular service. A benediction is the closing prayer of that service.
An invocation is a prayer asking God's help as part of a religious service. It is the first prayer offered at a church service. The last is called a Benediction.
I am not sure what prayer would, on its own, make anyone a Christian, since being a Christian is more about what you believe than what prayer you have said. I think that the question implies you no longer wish to be a Christian. If this is because you realise you do not believe in Christianity, then you are already not a Christian and have no reason to "take back" any prayer. However, if you were previously a member of another faith you may need to seek advice from your religious leaders about being readmitted to that faith.
A Mass always has the body and blood of Jesus made present by the priestat consecration; a prayer service does not.
There is no difference, it's two different words for the same thing.