"Sing all. See that you join with the congregation as frequently as you can. Let not a slight degree of weakness or weariness hinder you. If it is a cross to you, take it up, and you will find it a blessing." - John Wesley
This is one of my favorite of Wesley's points. We've all been in services in which participation is spotty. Many aren't singing, or at least aren't engaged enough to be engaged in full participation.
I've heard it said that if people aren't singing, they aren't worshiping. I'm not ready to affirm that statement entirely, but it does bring up a crucial point. If we are engaged in corporate worship, raising a collective voice in an offering to the throne of God, we need people to participate.
One of the problems with corporate singing is that it has fallen out of favor. Even when I was small, which really wasn't that long ago, it was a habit that was instilled into children (and still is in my classroom). This is sorely missed in corporate worship. If music is set up as more of a performance than a participatory activity, there really isn't any reason to participate. In fact, it's almost inadvertently discouraged. Congregants can just shift over into consumer mode, which is something all of us can do pretty easily these days. That means we have pews and sanctuaries full of disengaged people. If they are encouraged to sing at all, they're often encouraged to keep it an individual exercise, blocking out the mass that surrounds them. That's not the way to get people to follow Wesley's 3rd directive.
But we can all do it. Studies have shown that, with effort, nearly everyone can learn to sing on pitch and in rhythm. People just need encouragement. And they need to understand what they're being asked to do.
Another problem is that people don't understand more complicated hymn texts like they used to. It's very difficult to ask people to sing something that they can't understand. Therefore, congregations need to be immersed in biblical and theological education. They have to know what they're singing if they are to fully participate.
To the congregants, follow Wesley's words. Engage your mind and heart to form the words and manufacture the pitches. It doesn't have to be perfect, just heartfelt and authentic. Even if it's difficult, there's a huge blessing found in the sacrifice.
To the pastors, ministers and music directors, be an encouraging presence in your congregations. Get excited about what you're doing and show you exuberance for the truths you're asking congregants to sing. Above all, be enthusiastic and edifying educators in your congregations.
To God all praise and glory.