The denial of everything that interferes with intimate, direct fellowship between the life and God. We may have our symbol of fasting if we like, in a day in which we eat no food; but that is by no means essential. Fasting is a matter far deeper, far profounder. It is the life suffering the loss even of rights in order that it may come into more strenuous relationship with God. That is the deepest means of grace, and in proportion as we learn what fasting really means, we approach the infinite sources of power. G. Campbell Morgan concerning Matthew 6:16.
“Moreover when ye fast, be not, as the hypocrites, of a sad countenance: for they disfigure their faces that they may appear unto men to fast. Verily I say unto you, they have their reward.”
(Israel) One of Daniel's which lasted 3 weeks in 10:2-3 "I did not eat any tasty food, nor did meat or wine enter my mouth, nor did I use any ointment at all, until the entire three weeks were completed."
As to the Christian - Matt. 9:15 The fast is here mandated for the "friend of the Bridegroom" (NASB) who is known to be Israel."And Jesus said unto them, Can the children of the bride chamber mourn, as long as the bridegroom is with them? but the days will come, when the bridegroom shall be taken from them, and then shall they fast."
The Bride is not in the same state as the friend. She has His presence with her until His return. (Matt. 28:20)"Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you alway, even unto the end of the world."
Christ has ascended back to heaven, but He is present in every believer in the person of the Holy Spirit (John 14:16-17).
"And I will pray the Father, and he shall give you another Comforter, that he may abide with you for ever. Even the Spirit of truth; whom the world cannot receive, because it seeth him not, neither knoweth him: but ye know him; for he dwelleth with you, and shall be in you."
Not so for the friend who says they are awaiting His first coming. They lack the continual presence of the Son and The Holy Spirit. Cf. Luke 17:22. Fasting will come in the days of the Great Tribulation for the friend of the bridegroom."And he said unto the disciples, The days will come, when ye shall desire to see one of the days of the Son of man, and ye shall not see it."