The last thing the Church used to unite during the Roman persecution was liturgy. They came up with a team name, Catholic, creeds, the New Testament canon, and lastly, a common liturgy.
This is probably my favorite part of high church and something I would love to replicate in church. It would not be so stoic, but would be relevant and Scriptural. I think so far, the only thing I have is teaching catechism to the children. I hope what they learn lasts.
But there is just nothing more edifying than singing Scripture and reading it responsively. It was what I loved most in the Spring when I would go to the monastery and sing with the monks. When I visit Missouri Synod Lutheran churches up in Illinois, I loved that too. I hope some of that comes back in the Presbyterian Church, not as a rote practice, but as something that is explained.
The thing about liturgy is that the bishops developed a year-long Scripture reading and reflection to enable all the congregations in the known world to worship God in unison. I even remember 6 years ago a story of a man who stayed with the Roman Catholic church just because he knew if he went to another town, they would teach the same thing. I don't know if I'm so concerned about all our churches teaching the same thing, but I do want us all to teach the same Scriptures and the same doctrines which they give us. Maybe Presbyterian denominations should issue out daily readings and even hymns for families to do together at home. Maybe we should proclaim parts of the Westminster Confession of Faith each week as the Apostles' Creed is kind of vague. There will still be differences in interpretation, but we'd have unity in the essential beliefs.