Excerpted from the Handbook for Church Servers of Sergei Bulgakov:
The Holy Church calls the second Sunday of Great Lent the Sunday of the light creating fasts. In its Divine services, in line with the destruction of the sinful condition of man, it is descriptively and touchingly represented in the church hymns, which explains the Gospel parable about the Prodigal son, and praises the fast as a means to the beneficial inner light, and posits in this glorification a new impulse for the ascetic effort of the fast. The Orthodox teaching about fasting as a means for the beneficial inner light is opened with special power in the commemoration on this Sunday of St. Gregory Palamas, Archbishop of Thessalonica and Wonderworker. St.. Gregory is known as the one who exposed the heresy of Barlaam, the Calabrian monk, who rejected the Orthodox teaching about the blessed light, which illuminates the internal person sometimes openly visible (as for example on Tabor and Sinai), and who did not admit the possibility to achieve this inner light through both prayer and fasting and other individual efforts). At the Council in Constantinople called in 1341 concerning this heresy Barlaam, his disciple Akindynos, and their other accomplices were condemned for this false teaching. And during the subsequent time of his life St. Gregory zealously struggled for Orthodoxy, "not once", but "many times many" through his inspired speeches and writings denying the teachings and compositions of the evil followers of Akindynos and Barlaam. For this ascetic effort for the benefit of the Holy Church, and also for the confession and witness for the faith and Christ's flock, for the sanctity of the strict ascetic life and the deep edification for all ascetics through his works, St. Gregory is also glorified in the service on this day by the Holy Church.
From the Lenten Triodion:
What hymns of praise shall we sing in honour of the holy bishop? He is the trumpet of theology, the herald of the fire of grace, the honoured vessel of the Spirit, the unshaken pillar of the Church, the great joy of the inhabited earth, the river of wisdom, the candle-stick of the light, the shining star that makes glorious the whole creation.
What words of song shall we weave as a garland, to crown the holy bishop? He is the champion of true devotion and the adversary of ungodliness, the fervent protector of the Faith, the great guide and teacher, the well-tuned harp of the Spirit, the golden tongue, the fountain that flows with waters of healing for the faithful, Gregory the great and marvellous.
With what words shall we who dwell on earth praise the holy bishop? He is the teacher of the Church, the herald of the light of God, the initiate of the heavenly mysteries of the Trinity, the chief adornment of the monastic life, renowned alike in action and in contemplation, the glory of Thessalonica; and now he dwells in heaven with the great and glorious martyr Demetrius, whose relics flow with holy oil.
Inspired by the divine Spirit, as a winged angel thou hast come to the aid of the pious Emperor, fighting against the foolish-minded Barlaam, who in his madness blasphemed against the glory of God; and thou hast justly gained the victory over him.
Wholly filled with heavenly wisdom, O glorious saint, thou hast shone as a light in the world, teaching the doctrines of Orthodoxy. In thy love for true wisdom thou hast conceived the fear of God within thy heart, and given birth to the words of the Spirit.