9 Since then we have passed beyond that time of shadows, and no longer perform rites under it, but have turned, as it were, unto the Lord; 'for the Lord is the Spirit, and where the Spirit of the Lord is, there is liberty;'— as we hear the sacred trumpet, no longer slaying a material lamb, but that true Lamb that was slain, even our Lord Jesus Christ; 'Who was led as a sheep to the slaughter, and was dumb as a lamb before her shearers;' being purified by His precious blood, which speaks better things than that of Abel, having our feet shod with the preparation of the Gospel, holding in our hands the rod and staff of the Lord, by which that saint was comforted, who said, 'Your rod and Your staff they comfort me;' and to sum up, being in all respects prepared, and careful for nothing, because, as the blessed Paul says, 'The Lord is at hand;' and as our Saviour says, 'In an hour when we think not, the Lord comes—Let us keep the Feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth.
Putting off the old man and his deeds, let us put on the new man, which is created in God,' in humbleness of mind, and a pure conscience; in meditation of the law by night and by day. And casting away all hypocrisy and fraud, putting far from us all pride and deceit, let us take upon us love towards God and towards our neighbour, that being new [creatures], and receiving the new wine, even the Holy Spirit, we may properly keep the feast, even the month of these new [fruits].
Source: Letters (New Advent)