Notice that he says it's not enough to just believe (i.e. puts to rest the Protestant sola fide).
In other words, you must believe and receive the Holy Spirit through baptism, implying that the Holy Spirit is sacramentally present at baptism. That this is what the Church taught from the earliest can also be found in the West and the East, where the seal (chrism) is applied immediately after water baptism. In the Orthodox Church, this is done even to infants (their godparents believe and accept the Holy Spirit for them).
But those who don't believe are also not baptized and therefore they are lost.
Thus, Mark seems to suggest that faith is a requirement, but is not salvational without Baptism!
This is a very strange question for him to ask, since he himself taught that the Spirit comes with belief
I am a glad that I am not the only one who finds some thing strange with Acts.
I'm afraid sola fide is just fine with this. :) No one can truly believe unless he has already been baptized by the Holy Spirit. That is, in effect, the installation of faith, and so we believe. Sola Fide is secure. No one can "believe" without the Holy Spirit first acting, otherwise it is just "claiming" to believe. It isn't real.
Thus, Mark seems to suggest that faith is a requirement, but is not salvational without Baptism!
That's right! That IS what he's saying. He's just not talking about water baptism. :) A claimed faith without baptism of the Spirit is a false faith.