 As well as responding to attacks from the Catholic Church, in this period Luther began to face increasing challenges from his “own  people” within the reform movement   itself.[4]  Upon returning to Wittenberg from his relative seclusion, Luther found himself embroiled in controversies over the direction being taken by other figures such as Andreas Bodenstein von Karlstadt (1486–1541) and Thomas Müntzer (c. 1489–1525), and was caught up in associated theological disputes, while also facing growing political opposition. Luther preached the Invocavit (Lenten) Sermons which restored order to the city, and responded to his fellow reformers in A Sincere Admonition by Martin Luther to all Christians to Guard against Insurrection and Rebellion (1522), and to some of these political difficulties in his pamphlet On Temporal [or secular: weltlicher] Authority: To What Extent it Should be Obeyed (1523), in which he drew a distinction between two kingdoms or empires (die zwei Reiche) in an attempt to make clear where he took the limits of the power of princes to lie. Now no longer a monk, he published On the Estate of Marriage in 1522, and himself married Katharina von Bora in 1525, after she had left her convent with other nuns, convinced by Luther’s arguments against monasticism. The marriage was a successful and happy one, and they were to have six children together, of whom two daughters were to die young, affecting Luther greatly. Meanwhile, theological and doctrinal disputes were to persist for the rest of Luther’s career, on issues such as the Eucharist (or Lord's Supper: Heiliges Adendmahl) and baptism, both within the evangelical movement involving figures such as the sacramentarian Karlstadt, and the Swiss reformers Ulrich Zwingli (1484–1531) and Johannes Oecolampadius (1482–1531), and outside it with the Anabaptists. On both issues, Luther resisted the accounts of these sacraments as having a mere symbolic value, often arguing that this viewpoint comes from an urge to put reason above the authority of scripture (see, for example, Against the Heavenly Prophets (1525, WA 18:62–125, 134–214/LW 40:79–223), That These Words of Christ, “This is My Body”, Etc., Still Stand Firm Against the Fanatics (1527, WA 23:38–320/LW 37:3–150), and Concerning Rebaptism (1528, WA 26:144–74/LW 40:229–62)). 