It’s one thing to know about God, another to declare Him yours. This verse is a bold, public commitment.
The word translated as "avouched" is powerful. It means to publicly declare, to affirm, or to own something as your own. In this context, Israel isn't just acknowledging God's existence; they are actively choosing and declaring, "The LORD is my God." This isn't a passive agreement; it's an active, intentional act of commitment. It’s like saying, "Today, I am making my stand. Today, I choose Him, and by His grace, I will live as if He is indeed my God."
This declaration has weight. It’s a public affirmation of covenant. When you embrace God's covenant through faith in Jesus, you are also making this "this day" declaration. You are avouching Him as your God, setting Him apart from all others.