Tunichtgut is right. "In mari via tua" is Latin and literally means "your path through the sea" (so the Bibel's one is a good translation... you know, sometimes it's a bit inerpreted).
Some technical detail:
"mari" is the ablative form of "mare, maris" (3rd declination, neutral); "in"+ablative is often a place indication (and so it's here, but normally it's used to set state situation, not moving actions - for these we usually use "in"+accusative, which would be "in maria" using the plural form to indicate the whole ocean as commonly.)
"Via" is the nominative (subject) form of "via, viae" (1st declination, female), which means path, way (also metaphoric meaning), or even road as well.
"Tua" is the possessive adjective used for singular female things belonging to [you, 2nd person singular].
It's not Polish however... :)