Fasting

What is "fasting" (Acts 13:1)?
Fasting is intentionally abstaining from food for a period of time.

Why?
The human body is normally sustained by and draws energy from food. Fasting forgoes food and sometimes even water, and thereby requires drawing only on the far more powerful spiritual sustenance and energy directly from God. Fasting is usually accompanied by prayer.

Who were fasting above?
"Barnabas, Simeon who was called Niger, Lucius of Cyrene, Manaen ... and Saul" (Acts 13:1).

Why were they fasting?
They were "ministering to" (Acts 13:1) - i.e., serving - "the Lord" (Acts 13:1, see below).

What other purposes are linked to fasting in the Bible?
Another purpose of fasting is to plead in desperation to God. For example, 2 Samuel 12:16 records David fasting as he pleads for the life of the child he with Bathsheba after he committed adultery with her and murdered her husband: "David therefore pleaded with God for the child, and David fasted and went in and lay all night on the ground." It should be noted that fasting does not automate a positive answer from God, who still answers as per His holy and sovereign will. Another purpose of fasting is to cast out a certain "type" of demon: "And when they had come to the multitude, a man came to Him, kneeling down to Him and saying, “Lord, have mercy on my son, for he is an epileptic and suffers severely; for he often falls into the fire and often into the water. So I brought him to Your disciples, but they could not cure him.” Then Jesus answered and said, “O faithless and perverse generation, how long shall I be with you? How long shall I bear with you? Bring him here to Me.” And Jesus rebuked the demon, and it came out of him; and the child was cured from that very hour. Then the disciples came to Jesus privately and said, “Why could we not cast it out?” So Jesus said to them, “Because of your unbelief; for truly I say to you, if you have faith as a mustard seed, you will say to this mountain, ‘Move from here to there,’ and it will move; and nothing will be impossible for you. However, this kind does not go out except by prayer and fasting" (Matthew 17:14-21). And still another purpose of fasting is to seek God's comfort during times of mourning: "The words of Nehemiah the son of Hachaliah. It came to pass in the month of Chislev, in the twentieth year, as I was in Shushan the citadel, that Hanani one of my brethren came with men from Judah; and I asked them concerning the Jews who had escaped, who had survived the captivity, and concerning Jerusalem. And they said to me, 'The survivors who are left from the captivity in the province are there in great distress and reproach. The wall of Jerusalem is also broken down, and its gates are burned with fire.' So it was, when I heard these words, that I sat down and wept, and mourned for many days; I was fasting and praying before the God of heaven." (Nehemiah 1:1-4) 

What does "they were ministering to the Lord" (Acts 13:2) mean?
λειτουργουντων (leitourgounton), the original Greek word translated "were ministering," stem from a root word that gives us the English word "liturgy" and means performing a religious service, which would include prayer (see Acts 13:3), speaking, worshipping with songs, etc.

Who said, "Set apart for Me Barnabas and Saul for the work to which I have called them" (Acts 13:2)?
The "Holy Spirit" (Acts 13:2), once again proving His personhood.

What was the work to which God had called Barnabas and Saul?
To go "away" (Acts 13:3) to proclaim the Gospel and plant churches.

Where are "Seleucia, ... Cyprus" (Acts 13:4) and "Salamis" (Acts 13:5)?
Seleucia was the port city 15 miles (24 kilometers) down the Orontes River from Antioch, where the river emptied into the Mediterranean Sea. Cyprus is the island in the northeastern Mediterranean Sea that is about 100 miles (160 kilometers) southwest of Seleucia, and Salamis was a city on the east coast (facing Seleucia) of Cyprus.

Why did they preach "in the synagogues of the Jews" (Acts 13:5)?
Synagogues were where theology was discussed, and since the Jews already knew the Old Testament prophecies about the Messiah, they should have understood and received Jesus, a Jew, as the promised Messiah easier and quicker than the gentiles.

Who was Barnabas and Saul/Paul's "assistant" (Acts 13:5)?
"John" (Acts 13:5) "whose surname was Mark" (Acts 12:25), who was "the cousin of Barnabas" (Colossians 4:10) and who had accompanied Barnabas and Saul/Paul from Jerusalem.