The following site states where you can write for the records for the church at Gross Sabow:
Landeskirchliches Archiv der Pommerschen Evangelischen Kirche
Email address: email@example.com
Contact: Diplomarchivarin Ulrike Reinfeldt
Here is the website for the archives:www.pommersches-kirchenarchiv.de/
One important bit of information you should note is that only about 17% of church registers in Hinterpommern (that area of Pommern east of the Oder River and now in Poland) survived World War II. You are indeed very fortunate that the records for the church at Gross Sabow, Kreis Naugard, have survived. Please note the hours and days the archives is open, if you plan to visit.
Groß Sabow records are on microfilm and they have the following records available:
1708-1766 Baptisms, marriages & deaths
1773-1829 Baptisms, marriages & deaths
1830-1835 Baptisms, marriages & deaths
1836-1847 Baptisms, marriages & deaths
1848-1885 Baptisms, marriages & deaths
Congratulations on being one of the very few fortunate people who may find your Hinterpommern ancestors. Civil registration began in 1874 and I would direct any questions about those records to the Archives.
And be prepared for variations in the spelling of Jahnke. There are about 5 different ways to spell it.