Today's idea is beautiful and poetic, but it will be even more powerful for us if we understand its beauty. To do so, I think we need to understand the idea of our heart "beating in" or "beating with" something. Let's look at some other examples from the Course:
Two voices raised together call to the hearts of everyone, to let them beat as one. And in that single heartbeat is the unity of love proclaimed and given welcome. (T-20.V.2:3-4)
Imagine everyone's hearts beating as one. Imagine being in a stadium full of people standing completely silent and still, and in that silence, imagine hearing and feeling everyone's hearts beating together. What would you feel? I expect you would feel a tremendous sense of unity. You may even feel what the above quote says, that this single heartbeat proclaims "the unity of love." Why would it feel that way? Because, I think, our physical heart is a symbol for the heart of our being, the core of what we are. Thus, if our heart is beating in unison with others, then it feels like our very core is in rhythm with theirs, in harmony with theirs, united with theirs.
This world you bring with you to all the weary eyes and tired hearts that look on sin and beat its sad refrain. (T-25.IV.3:2)
Here is an image that is as negative as the first was positive. If your tired heart is beating sin's sad refrain, what does that mean? It means that at the heart of you (or what you think is the heart of you), you are in tune with the sad chorus of sin. Your heart is singing its song, joining its chorus. So the (seeming) core of you is joining itself to sin, in tune with sin, in unison with sin.
Look forward, then; in confidence walk with a happy heart that beats in hope and does not pound in fear. (T-30.V.10:8)
If your heart beats in hope, it's like the heart of you is filled with hope. If it pounds in fear, it's like fear has taken over your very core.
As you take the role assigned to you, salvation comes a little nearer each uncertain heart that does not beat as yet in tune with God. (W-pI.169.11:5)
The "uncertain heart" here is one that stands apart from God, by itself, in a state of uncertainty, with no firm ground to stand on. This is contrasted with the heart that beats in tune with God. That phrase "in tune with" captures what I've been saying throughout—that by beating with something, your heart joins itself to that something. By beating in tune with God, the heart of you is in harmony with God, in unison with God.
So now we have two musical allusions: your heart beating sin's sad refrain and your heart beating in tune with God. These are nice windows onto the overall concept. Talking about your heart's music is a way of talking about the tune that the core of you (or what seems like the core of you) is singing. However, it's not making its own music. It is singing with a song that is already out there. It is joining itself to a larger chorus, and by doing so, making that larger song what fills it, absorbs it, captures it. It is at one with that song.
Now we can have a fuller understanding of what it means to say, "My heart is beating in the peace of God." It means, "The very heart of me is at one with the peace of God." Here are some more variations, inspired by the foregoing passages:
My heart is beating as one with the Heart of God.
My heart looks on peace and beats its serene refrain.
I walk in confidence with a peaceful heart that beats in God.
My certain heart beats in tune with God.
Now let's turn briefly to the body of the lesson. It tells an interesting and important story if we reorder its points somewhat.
To begin with, each one of my heartbeats is calling to God (1:7), calling out for my lost home. And every single one is answered, as God assures "me I am at home in Him" (1:7). Imagine this assurance coming in response to every single heartbeat of yours, which means coming every second of every minute. As a result, "Peace fills my heart" (1:3). "Each heartbeat brings me peace," as my heart serenely beats in the peace of God.
You'd think this was the end of it. I've arrived. The lesson is learned and the journey over. But it's not. There is a larger picture going on, in which I have a part to play.
In this picture, every created thing is calling to me. Each heartbeat of each living creature calls my name, asking me to bring it peace. As the Text says, "Nothing but calls to you in soft appeal to be your friend, and let it join with you" (T-31.I.8:2). But I have been deaf to this call. "And so you did not hear it, and had lost a friend who always wanted to be part of you" (T-31.I.8:7).
Now, however, as my heart beats in God's peace, I can at last hear this universal call, and I can at last answer it. "Now my mind is healed, and all I need to save the world is given me" (1:4). Now the peace that fills my heart also "floods my body with the purpose of forgiveness" (1:3). My body is filled with the energy to bring forgiveness to all living things. "Each breath infuses me with strength" (1:5). And with this strength, I devote myself to passing on to all beings the peace that I have found. Just as I am "held forever quiet and at peace within His loving Arms" (1:6), so I take them by the hand and gently walk them back into those same loving Arms.
My peace has not drawn me into my private oasis. It has drawn me out of my shell, to go out and answer everyone's call to peace. Now that my heart is beating in tune with Him, "I am a messenger of God" (1:6).