Luther’s foundational belief was that we are saved only by the grace of God, not by our works as the Church had come to emphasize in his time. This meant that the individual had a direct line to God through which God’s grace was extended, not via the ecclesiastical system but through Jesus himself. Additionally, Luther argued that almost all “callings” had equal value through faith before God (a few vocations are excluded from this). In other words, we are all Christians and there doesn’t need to be and shouldn’t be a division between the spiritual and temporal: that’s why he condemned the monastic vows and commended life outside the isolation of the monastery. It doesn’t matter what one does but how it is done: to love other’s within their calling.
Francis De Sales was a Catholic who affirmed many of the ideas of faith in the ordinary life instead of the monastic pursuit. He oriented around simple steps of devotion anyone could take and like Luther, it was based on the idea that the foundation of this was love. He explained that it wasn’t as hard to get to heaven as many were told, and that it was more a series of steps toward purification and growth than maintenance of that state. This deviates from Luther, I believe, in being more works based than grace based but still has much more grace in it than I think they were used to at this point. Francis was totally confident in the redeemable nature of humans and God’s overflowing love, that we have a natural drive towards this love. Francis saw nature and grace as a merged attribute. Finally, Francis De Sales does tend to come across as a path that seems more about the individual than Luther, with charity being more surface and compassion having less depth. This is a first impression. I think this would be difficult to really discern without further research.
As I read about Francis De Sales I can see why it appeared more people turned to monastic callings from his teachings than Luther’s. Francis seems less concerned about division from each other and God and more concerned about the journey toward God. Luther seemed much more concerned about the division he saw for some people between God and those people, because of the journey of other’s towards God (in other words, the monastic and ecclesiastic groups within the Catholic Church).