Below is a very good insight from 'St. Jack'. By the way, I often say the prayer that he mentions, “Lord I believe, help Thou my unbelief.” In fact for several years now I have said it at the elevation of the Body and Blood of Christ during the Mass. (Update: after publishing this I realized there should be some clarification. I do not say this prayer in an audible voice. Instead, it is my own private devotion within the Mass.) Please don't misunderstand – it is not that I don't truly believe that it is our Lord's Body and Blood I hold in my hands – I pray it because I want my faith to be continually increased through the supernatural gift of grace we receive in the Most Holy Sacrament of the Altar. And it has had an effect on me.
Don’t bother at all about that question of a person being ‘made a Christian’ by baptism. It is only the usual trouble about words being used in more than one sense. Thus we might say a man ‘became a soldier’ the moment that he joined the army. But his instructors might say six months later ‘I think we have made a soldier of him’. Both usages are quite definable, only one wants to know which is being used in a given sentence. The Bible itself gives us one short prayer which is suitable for all who are struggling with the beliefs and doctrines. It is: ‘Lord I believe, help Thou my unbelief.’ Would something of this sort be any good?: Almighty God, who art the Father of lights and who has promised by thy dear Son that all who do thy will shall know thy doctrine: [John 7:17] give me grace so to live that by daily obedience I daily increase in faith and in the understanding of thy Holy Word, through Jesus Christ our Lord. Amen.
From The Collected Letters of C.S. Lewis, Volume II