I just don’t think an exhotation that “you must come to Mass every Sunday” on Christmas and Easter is going to rope that many people back to the pews. There is the saying, “you have to crawl before you can walk.” Get these people coming once a month. Then encourage twice a month, and then before long, you could have them back and attending.
People want community in their faith life. Look at the mega-non-denominational churches. Why do they lure so many people in? They feel like they belong to a community.
If the regular attendees and the pastor made the effort to foster a sense of belonging and community with the people who only come twice a year, I suspect that it wouldn’t be too long before they became regular attendees.
This doesn’t need to take away from or supplant the Sacrifice of the Mass, or the Catechism, or the holiness of the churches. Look to the East, and see what they do. A lot of Eastern Catholic and Orthodox Churches have “coffee hour” after the Liturgy, or sometimes a parish-wide meal.
A lot of our Protestant brethren do this too (I’ll bet they stole it from the East).
What are we doing to bring these people back?