saw the star. Supply the Ellipsis from Matthew 2:9 (App-6). "having seen the star [standing over where the young child was], they rejoiced", &c.
rejoiced with... joy. Figure of speech Polyptoton (App-6), for emphasis.
Related Commentaries of Matthew 2:10
Matthew 2:10
10 When they saw the star, they rejoiced with exceeding great joy.