Fasting is so powerful that Satan does not want a saint of God to do it. Just as God's systems and teachings answers problems related to sin in the flesh, Satan's system answers problems related to the righteousness of God dwelling in us.
Satan's answer is an affliction. Look at Mark 4.
13: And he said unto them, Know ye not this parable? and how then will ye know all parables?
14: The sower soweth the word.
15: And these are they by the way side, where the word is sown; but when they have heard, Satan cometh immediately, and taketh away the word that was sown in their hearts.
16: And these are they likewise which are sown on stony ground; who, when they have heard the word, immediately receive it with gladness;
17: And have no root in themselves, and so endure but for a time: afterward, when affliction or persecution ariseth for the word's sake, immediately they are offended.
18: And these are they which are sown among thorns; such as hear the word,
19: And the cares of this world, and the deceitfulness of riches, and the lusts of other things entering in, choke the word, and it becometh unfruitful.
20: And these are they which are sown on good ground; such as hear the word, and receive it, and bring forth fruit, some thirtyfold, some sixty, and some an hundred.
21: And he said unto them, Is a candle brought to be put under a bushel, or under a bed? and not to be set on a candlestick?
22: For there is nothing hid, which shall not be manifested; neither was any thing kept secret, but that it should come abroad.
23: If any man have ears to hear, let him hear.
The ground you walk on
Three of the four produced outcomes do not please God. Their reactions to affliction, suffering, and managing this worlds goods extracted whatever word the Lord shared with them.
What does this look like in real life?
Remember, the word of God, his laws and his statutes are holy and cannot be known by natural means.
A person "by the way side" indicates a person who was not the direct recipient of the word of God, so when they heard the word, Satan came immediately to take away the word and he succeeded.
This is the position that most saints are in when they listen to for example, preaching. They were not the direct recipient of the word of God, such as, David, Job, Peter and etc. This type of person never has an opportunity to experience the changing affects God's word has on their heart.
In verse 17, this person was a direct recipient of the word of God. A direct recipient is someone who prayed, God heard them and he has instructed them how to behave so that the outcomes from their behavior creates the blessing. In this case the saint did not make an effort to root themselves in the instructions of God. So, as time passed, they forgotten what God said.
Change will always challenge you
Note: Change will always challenge you and bring with it some form or level of persecution and/or affliction.
For example: if you were raised to spend money and not save, then you cannot save money. When you decide you want to save money, you will begin to discover opposition. This opposition doesn't exists in the money, it exists in you. Your entire lifestyle has been built around NOT saving money. Everything around you will challenge that change.
This idea works for the Word of God entering into the heart (mind). Your experiences are important to you because they help you make decisions. Most people don't like pain and often the pain that comes with change is too great for most people. So they leave it alone.
You see this outcome in saints who can't keep anything. They ask God for something and what they prayed for comes, but is lost later on. These are consistered unstable people or double-minded. They have this world's knowledge AND the knowledge of God, but are trying to make them both work. They are trying to be comfortable while creating change, and that is not a possibility. For a child of God this is a dangerous behavior. You cannot leave sin in place while trying to do service to God.
In verse 19, this is a person who has this world's goods. A rose is a beautiful flower to gaze upon, but the thorns can be pretty painful to touch. From an external point of view, this person has it all together. Nice car, expensive house and a high paying job. When the word of God comes directly to this saint, they immediately try to fit the Word into their lifestyle. They try to do this so that there would be no lost to what they own. So the word of God is constraint or restricted. As Mark says, it is choked and they bear no fruit in God.
Physically this person appears to have the righteousness of God in them because, at one time or another, God instructed them directly. They believe this world's goods are evidence that the Lord continues to lead them. But they have no fruit in them from God. The Lord is not ordering their steps. The Lord is not the author, nor the finisher of their faith.
The right way to handle the word
Now the most interesting part, what does bearing fruit in God look like?
This person hears the word of God, abides in Jesus Christ, and then works diligently to create various experiences in him in order to react or respond to that event in a way that pleases God.
Because we don't see things as clearly as we should, our response to God may not be perfect. So do what little bit you believe God wants from you, then observe the outcome from your responses. Patience is important here because some things do not provide immediate feedback, while others are immediate.
After you have done all to stand, stand. Grace is provided as a tool for you to use during periods of change. Why? Because you're going to make mistakes.
When God gives you one thing to do, oftentimes your natural thinking injects additional conversation and directives. When this happens, we will make mistakes. Grace is there to cover us, and the Holy Ghost to comfort us as we navigate the situation.
In the end, you will become more aware of how God thinks about a particular behavior. Your life, in that particular area, becomes more stable and when trials and tribulations come to take you through; you're like David says, "a tree planted by the rivers of water, that bring fruit in its season".