‘And Joshua said to the people, “You are witnesses against yourselves that you have chosen for yourselves Yahweh serve him.”
This was now a solemnising of the solemn covenant. It was like asking response to the marriage vows, the important words that seal the covenant. Once repeated it would be impossible to withdraw. They had stated that they would serve YHWH and Him alone. Now he called on them to act as witnesses to their own declaration.
‘And they said, “We are witnesses.”
Their response was a solemn avowal of what they had committed themselves to.