The word "marvel" is used very few times in the Bible when it comes to Jesus. I can see only two times when He actually marveled. Let me explain first of all, that the word "marvel" is thaumazō and it is used in terms of wonderment and even with a hint of admiration in this case, accrding to the dictionary. The situation here where the Savior is taken aback is when the Roman centurion shows such humility that he begs Jesus not only to heal the centurian's dying servant, he begs Jesus not to bother Himself with traveling and entering his home (Jewish belief at the time was that a Jew who entered a Gentile's home was ceremonially unclean).
The centurian only asks that Jesus says the words of healing, and the servant will be cleansed of his terminal illness.
Jesus is in wonderment at this man's amazing belief. This Roman has a faith that is absolutely stunning.
Yet Jesus wonders another time... in Mark 6:6 He wondered at His own people's unbelief.
And this gets me to thinking...
...I clearly recall in the 80s of the Lord caring for my every penny whenever, as a single man, I traveled the country as a small-time evangelist, speaking at churches and schools without ever asking for a cent. I commited to the Lord that if He wanted me to keep traveling, He would provide without me ever having to ask for money. For two years I ringed the United States speaking at churches as few as 20 and as large as 2,000. I never had to ask for support...that was a beautiful testing of my faith in which God came out more glorious than ever.
So why does my unbelief pop up now and again?
Jesus must wonder.