What is Martin Luther's approach to liturgical services in light of Paul Tillich? This article has a line that reads:


  We would call Luther's approach an evangelical-catholic one.


It cites Paul Tillich's use of "catholic substance" or "protestant principle". Can someone briefly summarize this concept in regards to Luther's approach to conducting liturgies or ceremonial worship? In what ways did Luther criticize the Roman Mass?

Is it trying to talk about Luther's protestant principle in regards to the catholic substance of the Catholic church during Luther's time?

I realize that the following resource may be helpful. 


  Obedient Rebels: Catholic Substance and Protestant Principle in Luther's Reformation. By Jaroslav Pelikan. 
  
  Dr. Pelikan both deepens our understanding of the Lutheran Reformation
  and contributes greatly to modern ecumenical dialogue. He describes
  "Catholic substance" as ". . . the body of tradition, liturgy, dogma,
  and churchmanship developed chiefly by the ancient church and embodied
  (but not exhausted) for Luther in the Roman Catholic Church of his
  day." "Protestant Principle" is understood as "the criticism and
  reconstruction of this Catholic substance . . . carried out in the
  name of the Christian gospel and with the authority of the Bible." For
  this union of "Catholic Substance" and "Protestant Principle" resulted
  the Protestant Reformation.
I think the answer can be found in the article you have linked.

On Page 129 for example, there's a description of how Luther broke up the unity of the eucharistic prayer:


  Luther's recension of the Canon of the Mass is more controversial.
  How much Luther can be held responsible for  breaking up the unity of
  the eucharistic prayer and how much  late medieval additions had
  already destroyed its unity is  debatable. Luther admitted there were
  sacrificial aspects of the  Eucharist. However, he judges Roman
  Catholicism's stress on  the Eucharist as "a good work we offer to God"
  to be totally wrong. In his Treatise on the New Testament, Luther
  states: "It  is not we who offer Christ, but Christ who offers us. . .
  . We  offer ourselves as a sacrifice along with Christ . . . he takes
  up  our cause . . . and offers himself for us in heaven. . . . We
  offer  our whole selves, our need, praise and thanks in Christ and 
  through Christ; and thereby (through faith) we offer Christ to  God,
  that is, we move Christ and give him occasion to offer  himself for us
  and to offer us with himself." Because it was offered silently,
  Luther could omit most of the Canon of the Mass without upsetting the
  people.


The rest of the paragraph you've quoted from page 127 I think gives us further context:


  We would call Luther's approach an evangelical-catholic one. He
  believes that unless God should provide a  better liturgy, the Church
  must stick as closely as is  evangelically possible to the liturgies
  of its past. Worship can and must express some continuity with the
  Church of the past,  since the Gospel had never completely vanished
  from it. In  short, Luther always remained closer to Rome than to the
  more  radical reformers who wanted to discard the historic church: 
  "Sooner than mere wine with the fanatics, I would agree with  the pope
  that there is only blood."


Luther wanted to return the church to the way he believed it existed anciently. His greatest criticism of Catholic mass was obviously the way it had changed from the Church of the past, which is largely contained in his famous 95 theses. 

In short, Luther preached the way he believed the Church of the past practiced. He took the tradition, liturgy, dogma, etc, of the Church (catholic substance)  criticized it (95 theses) and reconstructed it (protestant principle) then preached his reconstructions, which he believed to be what the Church preached anciently.