Unknowingly they lead us to joy

In his exposition of John 15:2, Martin Luther quotes an ancient hymn about the martyrs.

The world, to be sure, intends to do us harm, but it really accomplishes no more than what the church sings about the martyrs: “Unknowingly they lead us into eternal joys.” Unknowingly and involuntarily the world leads the Christians through torture and death to eternal joys. Such tortures are nothing else, as St. Agatha said, than taking our arms in a friendly way and leading us to heaven as a bride is led to a dance. Whatever harm is done to Christians by the world, God turns back their anger and lets the harm redound to their advantage.
(LW 24:196-197, On John 15:2 c. 1537)
And Take They Our Life: Martin Luther’s Theology of Martyrdom, Bryan Wolfmueller, 45

This is a profound spiritual mystery, that the devil unknowingly blesses us and carries us along to Jesus.

Pr Sean Kilgo found the hymn. He writes:

This is apparently an anonymous composition honoring St. Thomas Becket, the martyred Archbishop of Canterbury.

English Translation:

With the hope of reward and a crown,
Thomas stood ready for the contest,
obedient even unto death.
Imitating Christ in death,
confident and firm in faith,
he advanced with steady steps.
The martial furor seethed
as the holy man at the holy altar
was offered as a sacrifice.
The raging soldiers kill him
not knowing that they were leading
him to eternal joy.
He is the brave champion of Christ
who did not hesitate
to suffer death with joyful courage.
So that there might be salvation for the infirmed
and healing power for sinners,
he earned grace.
The blind, the lame,
the deaf, the mute,
have been restored to wholeness
with divine clemency.
There is no sickness
which he does not cure
once the stubborn faithlessness of those sick
does not persist.
The enemies of Christ yield to Christ
when signs, demonstrations of faith,
follow upon signs.
Therefore let the martyr be called upon:
so that through him it might be granted to us
to be carried to celestial realms.
Amen.

Latin Text:
Spe mercedis et coronae
Stetit Thomas in agone
Ad mortem oboediens
Morte Christum imitatus
Fide firmus et firmatus
Firmo gressu gradiens.
Furit furor militaris
Ut vir sacer sacris aris
Immoletur hostia;
Quem occident saevientes
Introducunt nescientes
Ad aeterna gaudia.
Christi fortis hic athleta
Qui subire mente laeta
Mortem non abhorruit.
Ut sit salus infirmorum
Et medela peccatorum
Gratiam promeruit.
Caeci, claudi,
Surdi, muti,
Sunt ad usum restituti
Divina clementia.
Non est morbus
Quem non curet
Dum morborum non obduret
Tarda diffidentia.
Hostes Christi Christo cedunt
Signa signis dum succedunt
Argumenta fidei.
Ergo martyr invocetur
Ut per eum nobis detur
Ad superna provehi.
Amen.