The word cup is to be understood as the perfect grace of charity by which the strength for undergoing suffering for the name of Christ is infused. This is given in such way that even if the opportunity by which anyone may undergo suffering for Christ is lacking, there is still such great strength in the heart by a divine gift that nothing is lacking for putting up with punishment, scorning life and undergoing death for the name of Christ. This is well understood in that text in the psalm where it is said, “My cup overflows,” and he had just said before, “You anoint my head with oil.” What must be understood by “head anointed with oil” except a mind strengthened by the gift of the Holy Spirit? The shining quality of this oil is the unconquerable fortitude of spiritual grace by which the holy drunkenness is poured into the inner depths of the heart so that every affection of the heart, overcome, is consigned to oblivion. Filled with this drunkenness, the spirit learns to rejoice always in the Lord and to consign to contempt whatever he loved in the world. We drink this drunkenness when, having received the Holy Spirit, we possess the grace of perfect charity that drives out fear.
Fulgentius: Selected Works. The Fathers of the Church, Volume 95 (Washington: Catholic University of America, 1997), 557–8; quoted in Craig A. Blaising & Carmen S. Hardin, Ancient Christian Commentary on Scripture; Old Testament VII: Psalms 1–50 (Downers Grove: IVP, 2008), 182.