From the great, lucid, holy Benedict XVI (2008):
The Solemnity of All Saints came to be affirmed in the course of the first Christian millennium as a collective celebration of martyrs. Already in 609, in Rome, Pope Boniface iv had consecrated the Pantheon, dedicating it to the Virgin Mary and to all the martyrs. Moreover, we can understand this martyrdom in a broad sense, in other words, as love for Christ without reserve, love that expresses itself in the total gift of self to God and to the brethren.
This spiritual destination, toward which all the baptized strive, is reached by following the way of the Gospel "beatitudes", as the liturgy of today's Solemnity indicates (cf. Mt 5: 1-12a). It is the same path Jesus indicated that men and women Saints have striven to follow, while at the same time being aware of their human limitations. In their earthly lives, in fact, they were poor in spirit, suffering for sins, meek, hungering and thirsting for justice, merciful, pure of heart, peacemakers, persecuted for the sake of justice.
And God let them partake in his very own happiness: they tasted it already in this world and in the next, they enjoy it in its fullness. They are now consoled, inheritors of the earth, satisfied, forgiven, seeing God whose children they are. In a word: "the reign of God is theirs" (Mt 5: 3,10).
On this day we feel revive within us our attraction to Heaven, which impels us to quicken the steps of our earthly pilgrimage. We feel enkindled in our hearts the desire to unite ourselves forever to the family of Saints, in which already now we have the grace to partake. As a famous spiritual song says: "Oh when the Saints, come marching in, oh how I want to be in that number!"
May this beautiful aspiration burn within all Christians, and help them to overcome every difficulty, every fear, every tribulation!
Let us place, dear friends, our hand in Mary's maternal hand, may the Queen of All Saints lead us towards our heavenly homeland, in the company of the blessed spirits "from every nation, people and language" (cf. Rv 7: 9). And already now we unite in prayer in remembering our dear deceased, who we will commemorate tomorrow.
And here's an ecumenical prayer via FR5:
OmnÃpotens sempitérne Deus, qui nos ómnium Sanctórum tuórum mérita sub una tribuÃsti celebritáte venerári: quæsumus; ut desiderátam nobis tuæ propitiatiónis abundántiam, multiplicátis intercessóribus, largiáris.
Almighty and everlasting God, who has enabled us to honor in one solemn feast the merits of all Thy Saints: we beseech Thee, that, with so many praying for us, Thou wouldst pour forth on us the abundance of Thy mercy for which we long.
May the powerful intercession of Our Lady and the Saints be with us all. And be assured, the iron gates of Hell shall not prevail against the onslaught of the hosts of heaven.
Here endeth the Lesson,
LSP