The theme of this Sunday is the virtue of hope, and what should be our response to it.
The texts focus first on the situation of the Jews, who had nothing other than promises on which to pin their hope. The Introit (from Psalm 73) says:
"Have regard, O Lord, to Thy covenant, and forsake not to the end the souls of Thy poor: arise, O Lord, and judge Thy cause, and forget not the voices of them that seek Thee."
The Graduale repeats the same line, and it is developed more fully in the Epistle, which is from Galatians 3, and talks about the promises made to Abraham.
The Gospel picks up the theme in the Epistle of the contrast between the situation of Jews, reliant only on the promise of the Messiah, and ourselves, who have the reality with the story of Christ healing the ten lepers.
After obeying Jesus' instructions to show themselves to the priests (and undergo the appropriate rituals to verify their healing), only one, a Samaritan, returns to give glory to God. It is a reminder that although we still need the virtue of hope to orient us to heaven, we already have the healing God gives (the theme of the Secret) and the reality of Christ in the Blessed Sacrament (the Communio), for which we should give thanks.
The Offertory summarises that orientation: "In thee, Lord, have I put my trust; I said, thou art my God, my times are in thy hands."