Definition: A catechism is a summary or exposition of doctrine, traditionally used in Christian
religious teaching from New Testament times to the present. Catechisms are doctrinal manuals often in the form of questions followed by answers to be memorized. (Wiki)
If that doesn’t make sense to you, then this is how I understand catechism; it is a question and answer format for remembering what you need to know about what you believe. Essentially it helps you remember what you believe and why you believe it and allows you to communicate that effectively to others.
We believe the bible to be the truth, the whole truth and nothing but the truth, but in a conversation where someone might question the bible how can we answer intelligently. Voddie Baucham uses this statement which I am memorizing and find to be concise and to the point, I have broken it up to visualise it more clearly.
I believe the bible to be:
- a reliable collection of historical documents
- written down by eye-witnesses
- during the lifetime of other eye witnesses
- they report to us super natural events
- that took place in fulfillment of specific prophecies
- and claim that their writings are divine rather than human in origin
Where in the bible does it say this?
2 Peter 1:16-21 (ESV)
16For we did not follow cleverly devised myths when we made known to you the power and coming of our Lord Jesus Christ, but we were eyewitnesses of his majesty. 17For when he received honor and glory from God the Father, and the voice was borne to him by the Majestic Glory, "This is my beloved Son, with whom I am well pleased," 18we ourselves heard this very voice borne from heaven, for we were with him on the holy mountain. 19And we have something more sure, the prophetic word, to which you will do well to pay attention as to a lamp shining in a dark place, until the day dawns and the morning star rises in your hearts, 20knowing this first of all, that no prophecy of Scripture comes from someone’s own interpretation. 21For no prophecy was ever produced by the will of man, but men spoke from God as they were carried along by the Holy Spirit.
See Voddie Baucham’s sermon for more.
At last we have our little boy! 
