This Summer Lent is a preparation for the great feast of SS. Peter and Paul on June 29th. These two apostles are the two pillars of the Church. It is also related to what Jesus said in Matthew 9:15, in reply to the Pharisees’ complaint that the apostles were not keeping fast days according to the Law: But the days will come, when the Bridegroom shall be taken from them, and then shall they fast." So, since Christ has returned to heaven on Ascension, and since the tradition is that the disciples fasted for the nine days before Pentecost, the proclamation of the Gospel must be accompanied by prayer and fasting.
The summer fast once went from the day after All Saints Sunday to August 15, but the ByzantineChurch used the principle of “economy” (oikonomia) and broke it into the two separate fasts we have today.
The traditional Fast as described in the Typikon is one of strict abstinence on Monday, Wednesday, and Friday. In the United States, the Ruthenian Metropolia (to which branch of Byzantine Catholicism we belong) recognizes this as a penitential season but observance is voluntary.