And the prince of the eunuchs said unto Daniel, I fear my lord the king, who hath appointed your meat and your drink: for why should he see your faces worse liking than the children which are of your sort? then shall ye make me endanger my head to the king. Then said Daniel to Melzar whom the prince of the eunuchs had set over Daniel, Hananiah, Mishael, and Azariah, Prove thy servants, I beseech thee, ten days; and let them give us pulse to eat, and water to drink. Then let our countenances be looked upon before thee, and the countenance of the children that eat of the portion of the king's meat: and as thou seest, deal with thy servants. (Daniel 1:10-13)
The Bible tells us that Daniel's decision to refuse the Babylonian diet was something he "purposed in his heart." I want to comment for a moment on this issue of making Christian living and separation from the world a matter of a few little rules that have to do with eating and with conduct. There is always a tendency in this area to be dogmatic and forbid certain questionable things, things which are actually debatable.
I received a letter once from a lady who joined a small group shortly after she had become a Christian, and they told her there were certain things she couldn't do and certain things she could do. In the letter which she wrote to me she said, "I have followed all these rules, and yet I am still miserable."
In the history of the church we can see times when people set up a system of doing things and not doing things — systems that actually were good at first. For example, the monasteries which began in the Roman Empire were actually a protest against the licentiousness of their day. But before long it was worse on the inside of the monastery than on the outside.
Remember that Christ said to the Pharisees, "Now do ye Pharisees make clean the outside of the cup and the platter; but your inward part is full of ravening and wickedness" (Luke 11:39). In other words, "You make the outside of the cup clean, but inside it's dirty. It is just like whitewashing a tomb." Today it is "not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost" (Titus 3:5). In order to live a life of holiness, we must first receive new life from God - we must be born from above.
"Daniel purposed in his heart" (v. 8) — it all began in the heart of Daniel. He was not a papier-mâché; he had a heart, and his convictions came from his heart. That should be our experience also. We are captives in this world in which we live; gravitation holds all of us by the seat of our pants, and we cannot jump off this earth. The Lord Jesus said that we are in the world, but not of the world. And He said, "Ye cannot serve God and mammon" (Matthew 6:24). However, we cannot serve God by following a set of rules; we must have a purpose in our hearts. Jesus said that it was out of the heart that the issues of life proceed; the things which we put into our bodies are not the most important. Daniel purposed in his heart that he would obey God's law given to God's people Israel - this was to be his testimony.
—From Edited Messages on Daniel by Dr. J. Vernon McGee