The following is an excerpt from The MacArthur New Testament Commentary on Acts 2.

So then, those who had received his word were baptized; and there were added that day about three thousand souls. (2:41)

As already noted, much present day evangelism seeks to make coming to Christ as easy as possible. Many today would be appalled that Peter made the cost of coming to Christ so high. How could he expect them to turn their backs publicly on their culture? How could he ask them to risk becoming outcasts among their families and society? How could he demand that they accept as Messiah the very One their leaders had rejected and executed? They would no doubt predict that the results of Peter’s sermon would be minimal.

Such was not the case, however. Those who had received his word accepted the conditions and were baptized. Further, they amounted to more than an insignificant handful; there were added to the church that day about three thousand souls. That a precise number was recorded suggests that they kept track of those who were saved and baptized.