"I found something in New Zealand I had lost over a period of time, which was trying to be the best player on the field," Marshall said.
"I was playing for the sake of being there with my mates, and probably got a bit comfortable, and lost a lot of motivation.
"When I went to New Zealand, I had to prove myself again, which made me find a lot of things I thought I had lost, and that you don't think about when you've been in the same for so long.
"For me, going to New Zealand was the best thing I could have done."
With Manly five-eighth Kieran Foran under an injury cloud, Marshall is a chance to play his first test in three years.
Foran is a chance of playing in Manly's Anzac Day clash with the Storm in Melbourne but should he fail to recover from a hamstring injury in time, a resurgent Marshall could be in the frame to make a test recall after last donning the Kiwis jersey in 2012.