Complex sentence: During repolarization, voltage-gated sodium ion channels inactivate due to the now depolarized membrane, and voltage-gated potassium channels open both acting to repolarize (or hyperpolarize) the cell's membrane potential back to its resting membrane potential.
Split into simpler sentences: During repolarization, voltage-gated sodium ion channels inactivate (close) due to the now depolarized membrane, and voltage-gated potassium channels activate (open). Both the sodium ion channels closing and the potassium ion channels opening act to repolarize the cell's membrane potential back to its resting membrane potential.