Definition and Purpose:
Fasting, in the biblical context, refers to the voluntary abstention from food, and sometimes drink, for a specified period. It is often undertaken as a spiritual discipline to seek God's guidance, express repentance, or demonstrate earnestness in prayer. Fasting is a practice that appears throughout the Bible, serving various purposes such as mourning, seeking divine intervention, and spiritual renewal.

Old Testament Instances:
Fasting is first mentioned in the Old Testament, where it is often associated with mourning or repentance. In the Book of Esther, Queen Esther calls for a fast among the Jews before she approaches the king, saying, "Go, gather together all the Jews who are in Susa, and fast for me. Do not eat or drink for three days, night or day. I and my attendants will fast as you do" (Esther 4:16). Similarly, in the Book of Jonah, the people of Nineveh fast in response to Jonah's warning of impending judgment: "When the word reached the king of Nineveh, he rose from his throne, took off his royal robe, covered himself with sackcloth, and sat in ashes. Then he issued a proclamation in Nineveh: 'By the decree of the king and his nobles: Let no man or beast, herd or flock, taste anything at all. They must not eat or drink'" (Jonah 3:6-7).

New Testament Teachings:
In the New Testament, fasting continues to be a significant spiritual practice. Jesus Himself fasted for forty days and nights in the wilderness before beginning His public ministry: "After fasting forty days and forty nights, He was hungry" (Matthew 4:2). Jesus also taught about fasting in the Sermon on the Mount, emphasizing the importance of sincerity and humility: "When you fast, do not be somber like the hypocrites, for they disfigure their faces to show men they are fasting. Truly I tell you, they already have their reward. But when you fast, anoint your head and wash your face, so that your fasting will not be obvious to men, but only to your Father, who is unseen. And your Father, who sees what is done in secret, will reward you" (Matthew 6:16-18).

Apostolic Practice:
The early church also practiced fasting, often in conjunction with prayer, to seek God's will and empowerment. In the Book of Acts, the church at Antioch fasted and prayed before sending out Paul and Barnabas on their missionary journey: "While they were worshiping the Lord and fasting, the Holy Spirit said, 'Set apart for Me Barnabas and Saul for the work to which I have called them.' So after they had fasted and prayed, they laid their hands on them and sent them off" (Acts 13:2-3).

Spiritual Significance:
Fasting is seen as a means of humbling oneself before God, as expressed in Psalm 35:13: "Yet when they were ill, I put on sackcloth; I humbled myself with fasting." It is a way to draw closer to God, to seek His face, and to align one's heart with His purposes. The prophet Isaiah, however, warns against fasting as a mere ritual without genuine repentance and righteousness: "Is this the fast I have chosen, a day for a man to deny himself? Is it only for bowing one's head like a reed and for lying in sackcloth and ashes? Is this what you call a fast, a day acceptable to the LORD?" (Isaiah 58:5).

Conclusion:
Fasting, as depicted in the Bible, is a profound spiritual discipline that involves more than abstaining from food. It is an act of worship, a means of seeking God's presence, and a demonstration of earnestness in prayer and repentance. Through fasting, believers express their dependence on God, their desire for His guidance, and their commitment to His will.