Knowing that Christ being raised from the dead dieth no more; death hath no more dominion over him. When it is implied here that death had once dominion over him, it is not, of course, meant that he was in his own Divide nature subject to death, or that 'it was possible that he should be holden of it."
All that is implied is that he had made himself subject to it by taking on him our nature, and voluntarily submitted to it, once for all, as representing us (cf. John 10:17; Acts 2:24).