Interesting. I've not seen that quote. Lutheran theology does stress assurance and justification, but it also allows for the possibility of losing faith. That isn't talked about much, or at least that was my experience in being LCMS Lutheran.
Yes, that's true even for the ELCA. We don't talk about losing faith so much because we believe in using the law more for suggestion than coercion. We don't want to shatter consciences, we want to form them. Despair is the certain enemy of a living faith, all our good works come from a faith that is confident that God's promises are
pro me (for me).
We don't exactly believe in sinning so grace abounds. But neither do we believe in living in despair of our sins. In this life, we will sin. Because we are sinners, and in bondage to sin, and in daily need of acknowledging this, that Christ is our only hope. That quote about "sin boldly" is frequently misunderstood, it can only be understood from the context of despair over ones sins, and the promise that Jesus is indeed the Savior of real sinners. It is not to be taken too generally as the way Lutherans behave. We believe in good order and serving others, not in anarchy and self-interest.
Our ethics is serious and robust, but it differs substantially from some interpretations of the Reformed tradition, especially the Puritanism common in America that is a general feature of evangelicalism here.
It just so happens alot of those insights I was talking about, about forming consciences, are precisely the way a good therapist would interact with a patient, so they are confirmed by the modern insights of psychology. We are a proclamation oriented people, we are not a purity oriented people, and we want to sincerely offer to all people the means of grace and accompany them in faith. They are free to reject that of course, but we hopefully will not present stumbling blocks to faith, that would be a tragedy.
They seem extremely similar to me, except that Lutherans seem to reject the idea of "irresistible grace." What other major differences are there
The theologian Gerhard Forde was once asked about whether grace was irresistible. His reply was "I find grace irresistible, don't you?" I think that's the Lutheran attitude on the subject. We aren't dogmatic about it, but we aren't exactly big on the idea that Christians sit around and choose to respond to grace, like it's an intellectual exercise, like you have this "offer" from God that you need to consider. Christians do respond to the Gospel. How that happens, how much freedom we have in it, what it will look like in our callings, will be different for every human being.
The critique of the doctrine of irresistible grace has more to do with our concern that we do believe Christians can reject the faith and be lost. Some of our theologians have even taught that certain actual sins are so egregious, they could stem from departing from a living faith, and therefore could be considered "mortal". But I think that would be controversial and something not emphasized among modern Lutherans (there are still controversies in Lutheranism and different schools of interpretation, as in any church tradition).