From one of the sequences of Mass, these verses remind Jesus that he's already put a lot of effort into saving us!
The Dies Irae (Day of Wrath) is one of the poem-chants attached to a liturgical feast, in this case All Souls Day. It can also be used at funeral Masses.
While some of the verses, as the name implies, are sober reminders of the imposing reality of Judgment Day, the poem itself is a prayer for mercy.
Since none of us can claim innocence before the Just God, the chant reminds Him that he has put so much effort into saving our souls already, and beseeches Him to keep the blood He shed from being shed in vain.
As the liturgy points us to the end of the world and the end of our earthly lives with the coming conclusion of the liturgical year, these verses are healing and consoling words to take to prayer.
Remember, faithful Jesus, because I am the cause of your journey: do not lose me on that day. … Thou has sat down as one wearied seeking me, Thou has redeemed (me) having suffered the Cross: so much labor let it not be lost. … Among the sheep offer (me) a place and from the goats sequester me, placing (me) at (Thy) right hand.