Matthew 7:21-23 speaks of true and false converts. True converts are ones who naturally act as. opposed to false converts who also act per their nature, but are not truly converted.
Every tree, which you see later in the chapter, is known by it's fruits A good tree cannot bear bad fruits nor can a bad tree bear good fruits.
False converts cannot please or obey God becaus e they've never believed in the first place (1 Corinthians 15:3-4 & Romans 8:7). If such a Goat, "Judas", enters and mingles among the Sheep, and behaives like them, then time will reveal who he really is. And often it is through unrepentant sin he is revealed. Or, persecution. Either way, 1 John 2:19-20:
19 They went out from us, but they were not of us; for if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all of us.
But true converts, behaves like Sheep, because they are Sheep. When they're saved, they went from possessing a Carnal mind to being Spritually minded (Romans 8:6-7): slave to sin, to being a slave to righteousness (Romans 6:16-18), and this is possible because they're a new Creature (2 Corinthians 5:17).
New creature, new nature (1 John 3:6-9).
The evidence of their conversion, is a life of obedience; opposed to those who simply claimed to be (James 2:14-26), but are not.