The final chant after sitting is a dedication that any merit we gain from chanting the Heart Sutra is not retained by us, but is for the benefit of all beings. But really, the dedication is wider than that; it embraces our sitting too.
Our sitting is itself a devotional act. The doors of the heart are thrown wide open. And so, zazen is not the cultivation of compassion, it is its expression.
In this context, we can understand the first vow: “All living beings, I vow to save them”. Imagine the opposite: “I vow to save myself”. It’s not possible. You can’t save yourself, you can only postpone the catastrophe.
We are saved by the vow. It shelters us and all beings. All beings are saved.