The people of Hadeln, represented by their estates of the realm, adopted the Lutheran Reformation in 1525 and Duke Magnus I confirmed Hadeln's Lutheran Church Order in 1526, establishing Hadeln's separate ecclesiastical body existing until 1885.
Magnus did not promote the spreading of Lutheranism in the rest of his duchy.
Lutheran preachers, most likely from the southerly adjacent Principality of Lunenburg, Lutheran since 1529, held the first Lutheran preaches; at the northern entrance of St. Mary Magdalene Church in Lauenburg upon Elbe one is recalled for St John's Eve in 1531.
Tacitly, the congregations appointed Lutheran preachers so that the visitations of 1564 and 1566, ordered by Duke Francis I, Magnus I's son, on the instigation of the Ritter- und Landschaft, saw already Lutheran preachers in many parishes.
In 1566, Francis I appointed the Superintendent Franciscus Baringius as the first spiritual leader of the church in the duchy, not including Hadeln.

Francis I conducted a thrifty reign and resigned in favour of his eldest son Magnus II once having exploited all his means in 1571.
Magnus II promised to redeem the pawned ducal demesnes with funds he gained as a Swedish military commander and by his marriage to Princess Sophia of Sweden.
However, Magnus did not redeem pawns but further alienated ducal possessions, which ignited a conflict between Magnus and his father and brothers Francis (II) and Maurice as well as the estates of the duchy, further escalating due to Magnus' violent temperament.

In 1573, Francis I deposed Magnus and reascended to the throne while Magnus fled to Sweden.
The following year Magnus hired troops in order to take Saxe-Lauenburg with violence.
Francis II, an experienced military commander in imperial service, and Duke Adolphus of Schleswig and Holstein at Gottorp, then Lower Saxon Circle Colonel (Kreisobrist), helped Francis I to defeat Magnus.
In return Saxe-Lauenburg had to cede the bailiwick of Steinhorst to Gottorp in 1575.
Francis II again helped his father to inhibit Magnus' second military attempt to overthrow his father in 1578.
Francis I then made Francis II his vicegerent actually governing the duchy.

 In 1581 - shortly before he died and after consultations with his son Prince-Archbishop Henry of Bremen and Emperor Rudolph II, but unconcerted with his other sons Magnus and Maurice - Francis I made his third son Francis II, whom he considered the ablest, his sole successor, violating the rules of primogeniture.
This severed the anyway difficult relations with the estates of the duchy, which fought the ducal practice of growing indebtedness.

The general church visitation of 1581, prompted by Francis II, showed poor results as to the knowledge, practice and behaviour of many pastors.
Baringius was held responsible for these grievances and replaced by Gerhard Sagittarius in 1582.
Finally in 1585, after consultations with his brother Prince-Archbishop Henry, Francis II decreed a constitution (Niedersächsische Kirchenordnung; Lower Saxon Church Order), authored by Lübeck's Superintendent Andreas Pouchenius the Elder, for the Lutheran church of Saxe-Lauenburg.
It constituted the Lutheran state church of Saxe-Lauenburg, with general superintendent (as of 1592) and consistory seated in the city of Lauenburg, which merged into that of Schleswig Holstein in 1877.
Francis II's attempt to merge Hadeln's Lutheran church body with that in the rest of the duchy was unanimously rejected by Hadeln's clergy and estates in 1585 and 1586.

The violation of the primogeniture, however, gave grounds for the estates to perceive the upcoming duke Francis II as illegitimate.
This forced him into negotiations, which ended on 16 December 1585 with the constitutional act of the "Eternal Union" (German: Ewige Union) of the representatives of Saxe-Lauenburg's nobility (Ritterschaft, i.e. knighthood) and other subjects (Landschaft), mostly from the cities, Lauenburg upon Elbe and Ratzeburg, then altogether constituted as the estates of the duchy (Ritter- und Landschaft), led by the Land Marshall, a hereditary
The people of Hadeln, represented by their estates of the realm, adopted the Lutheran Reformation in 1525 and Duke Magnus I confirmed Hadeln's Lutheran Church Order in 1526, establishing Hadeln's separate ecclesiastical body existing until 1885. Magnus did not promote the spreading of Lutheranism in the rest of his duchy. Lutheran preachers, most likely from the southerly adjacent Principality of Lunenburg, Lutheran since 1529, held the first Lutheran preaches; at the northern entrance of St. Mary Magdalene Church in Lauenburg upon Elbe one is recalled for St John's Eve in 1531. Tacitly, the congregations appointed Lutheran preachers so that the visitations of 1564 and 1566, ordered by Duke Francis I, Magnus I's son, on the instigation of the Ritter- und Landschaft, saw already Lutheran preachers in many parishes. In 1566, Francis I appointed the Superintendent Franciscus Baringius as the first spiritual leader of the church in the duchy, not including Hadeln.
Francis I conducted a thrifty reign and resigned in favour of his eldest son Magnus II once having exploited all his means in 1571. Magnus II promised to redeem the pawned ducal demesnes with funds he gained as a Swedish military commander and by his marriage to Princess Sophia of Sweden. However, Magnus did not redeem pawns but further alienated ducal possessions, which ignited a conflict between Magnus and his father and brothers Francis (II) and Maurice as well as the estates of the duchy, further escalating due to Magnus' violent temperament.
In 1573, Francis I deposed Magnus and reascended to the throne while Magnus fled to Sweden. The following year Magnus hired troops in order to take Saxe-Lauenburg with violence. Francis II, an experienced military commander in imperial service, and Duke Adolphus of Schleswig and Holstein at Gottorp, then Lower Saxon Circle Colonel (Kreisobrist), helped Francis I to defeat Magnus. In return Saxe-Lauenburg had to cede the bailiwick of Steinhorst to Gottorp in 1575. Francis II again helped his father to inhibit Magnus' second military attempt to overthrow his father in 1578. Francis I then made Francis II his vicegerent actually governing the duchy.
 In 1581 - shortly before he died and after consultations with his son Prince-Archbishop Henry of Bremen and Emperor Rudolph II, but unconcerted with his other sons Magnus and Maurice - Francis I made his third son Francis II, whom he considered the ablest, his sole successor, violating the rules of primogeniture. This severed the anyway difficult relations with the estates of the duchy, which fought the ducal practice of growing indebtedness.
The general church visitation of 1581, prompted by Francis II, showed poor results as to the knowledge, practice and behaviour of many pastors. Baringius was held responsible for these grievances and replaced by Gerhard Sagittarius in 1582. Finally in 1585, after consultations with his brother Prince-Archbishop Henry, Francis II decreed a constitution (Niedersächsische Kirchenordnung; Lower Saxon Church Order), authored by Lübeck's Superintendent Andreas Pouchenius the Elder, for the Lutheran church of Saxe-Lauenburg. It constituted the Lutheran state church of Saxe-Lauenburg, with general superintendent (as of 1592) and consistory seated in the city of Lauenburg, which merged into that of Schleswig Holstein in 1877. Francis II's attempt to merge Hadeln's Lutheran church body with that in the rest of the duchy was unanimously rejected by Hadeln's clergy and estates in 1585 and 1586.
The violation of the primogeniture, however, gave grounds for the estates to perceive the upcoming duke Francis II as illegitimate. This forced him into negotiations, which ended on 16 December 1585 with the constitutional act of the "Eternal Union" (German: Ewige Union) of the representatives of Saxe-Lauenburg's nobility (Ritterschaft, i.e. knighthood) and other subjects (Landschaft), mostly from the cities, Lauenburg upon Elbe and Ratzeburg, then altogether constituted as the estates of the duchy (Ritter- und Landschaft), led by the Land Marshall, a hereditary 
Saxe-Lauenburg