Read verse 37 more closely. Peter preached. They heard...given understanding. Their hearts were pricked...circumcision of the heart. Their wills were altered...what shall we do?
They were born again by the word of God and the activity of the Spirit of God within them. Of course they responded in obedience. God uses Peter's sermon to bring enlightenment and the Spirit wrote those words on their hearts. That's the new covenant promise...Ezekiel 36:26-27.
Are you implying they were reborn in verse 37?
Are you implying they had the Holy Ghost in verse 37?