A pagan should become Catholic because otherwise he will go to hell!
#3 “
The most Holy Roman Church firmly believes, professes and
preaches that none of those existing outside the Catholic Church, not
only pagans, but also Jews and heretics and schismatics, can have a
share in life eternal; but that they will go into the eternal fire which
was prepared for the devil and his angels, unless before death they
are joined with Her; and that so important is the unity of this
ecclesiastical body that only those remaining within this unity can
profit by the sacraments of the Church unto salvation, and they alone
can receive an eternal recompense for their fasts, their almsgivings,
their other works of Christian piety and the duties of a Christian
soldier. No one, let his almsgiving be as great as it may, no one, even if
he pour out his blood for the Name of Christ, can be saved, unless he
remain within the bosom and the unity of the Catholic Church.”
(Pope Eugene IV, the Bull Cantate Domino, Council of Florence 1441.)
ewtn.com/library/councils/florence.htm