How much belief and faith do you need to be a Christian? There is a story about a father with a
demon possessed son who asked for help with his disbelief. Is a simply decision enough?
What does faith have to do with the story of the rich man who became disappointed when he
felt he could not give up his wealth ?
You asked many questions, some of them which are not listed above. I will try to give an appropriate response to them.
In answer to your first question, as to "How much belief and faith is needed to be a Christian", and your reference to this issue in the story of a demon possessed boy, this story has nothing to do with 'how much belief or faith' you must have to be a Christian. It has to do what is truly in your heart.
The story of the demon possessed boy is in Mark chapter 9, verses 14-29. The essence of the story is about a boy who is possessed by a demon that the disciples were unable to remove. Jesus points out the issue of their doubt;
"He answered him and said, "O faithless generation, how long shall I be with you? How long shall I bear with you? Bring him
to Me." Mk. 9:19
Then, the father of the boy's statement to Jesus was another key issue here. With Jesus standing there in front of him he said, "If thou canst do any thing, have compassion on us". Jesus responded with;
".....If you can believe, all things are possible to him who believes." Mk. 9:23
Here we see the fathers doubt in Jesus' ability. So to answer your question directly, it's not 'how much faith' but the quality of your faith.... Is it true? Do you honestly believe that Jesus is capable to be your Lord and Savior.
Your second and third questions essentially go together. In essence, your questions here are in dealing with what is required for salvation. They are common questions that we all have once we believe in Jesus Christ. I believe, it is this 'questioning' that we have that is an indication of God changing your heart, so that by His Grace your faith is built up;
"For by grace you have been saved through faith, and that not of yourselves; it is the gift of God, not of works, lest anyone
should boast." Eph. 2: 8
It is essential to understand, that is by this grace of God, that you are justified by faith alone. That this will allow you to turn to Jesus, asking for forgiveness of your sins, asking Him to come into your life and change you. Then you become a 'Child of God' accepting Jesus as your Lord and Savior. This is what the verse, of John 3:16 means where it says....."he who believes in Him, shall not perish, but have eternal life."
You also asked about what if you know you're not strong enough to give up things in your life? You aren't on your own. God knows your limitations. He will strengthen you to build your faith as you continue with you journey with Him. This is part of the 'gift' in the above verse in Ephesians is about.
Lastly you asked about the story of the rich man. This story (in Mathew Ch. 19 verses 16-28) involves Jesus' knowing the man's intentions because he knew what was truly in his heart. When the man asked which commandments he should follow in order to enter into eternal life, one of the commandments Jesus repeated was to "love thy neighbor as thyself. And when He told the man to sell all his possessions and give to the poor then follow Him. The man's true heart showed he was unable to do this.
"And again I say to you, it is easier for a camel to go through the eye of a needle than for a rich man to enter the kingdom of God." Mat. 19:24
Again, this comes down to the 'quality' of your heart's intentions, not the 'quantity'. God knows what you believe, even if you're unsure. Don't let the details of the 'exact type' or 'how much' of belief confuse you. Pray for guidance and strength. Pray for the understanding of his word and to build your confidence, and what you believe is true.
Remember one very important thing. God is as much of LOVE as He is justice. He knows us better than we know ourselves. He sees our Hearts, and if we truly believe in Jesus, we will truly love him even though we can not physically see Him. We will feel him in our hearts and see Him in the hearts of others. This, is called FAITH.