There is clearly inclusion here, not based on affiliation with the bloodline of Israel or any kind of ceremonial cleanness but on the individual's purposeful following of the one true God in faithfulness and according to His righteousness. God is the one who accomplishes salvation and brings righteousness, which either has to be experienced in the individual by the flawless adherence to every aspect of the perfect Law or by the mercy of God. Here that mercy is clear because the follower of God is expected to acknowledge God's perfect truth--no matter their personal failure to live up to it. Others will be gathered to Israel that are not of Israel (8), but the ones to whom the covenants of God were first made have shown themselves to be unworthy stewards of the promise. They are blind, mute, lazy (10), greedy, stupid, directionless, crooked (11) drunkards (12). That does not seem like a glowing commendation of the chosen ones.
Where Ch. 56 portrays the godly eunuch and foreigner against the ungodly watchman from the chosen people, Ch. 57 begins with an explanation from God of why the righteous die early (1-2). There are other texts that do not fit this 'mold,' so we cannot say this is the 'once and for all time' reality of early death. Obviously there are many ungodly people who die early, as there are many godly people who live long, and sometimes painful, lives (see the book of Job for a great discussion of this issue). But death, to be sure, ends the earthly struggle and, for the righteous, ushers in the eternal peace of rest in God. The person who is like this is juxtaposed with the behavior of the 'people' described in 56:9-12. God's chosen people, who tire themselves out with their rebellious adultery (3-9), deny God in their ways and find strength to continue in their evil ways (10). They didn't worry about things like consequences or acting in righteousness because nothing bad seemed to happen to them, God didn't immediately speak up (11-12). As a result, what little righteousness they possess is useless in protecting them, just like the idols they construct, but the ones who turn to God in reliance will inherit God's blessings (13). God will make a way for those who honor Him (14), for God is both "high and holy" and with the "contrite and lowly of spirit" (15). God's judgment against those He's chosen would crush spirits and remove their life if He didn't relent (16), but since His punishment is meant for their foolishness in turning away from Him and to restore them to praise of Himself, God will heal and bring peace (17-19). The wicked, on the other hand, will not find peace but will find their life stirring up all kinds of filth and crap, literally (20-21).
There is no way to separate the simplicity of God's word: God brings His salvation in revealed righteousness AND we are instructed to do what pleases God. Five-finger exercises and outlined salvation processes, though practical and helpful in a Sunday school setting, are ultimately incomplete guides to God. They are the Church's way of getting to the 'people' they reach out to what the 'people' want--in effect, a Clif's Notes version of God's ways and desires for us. We find throughout scripture the various instructions on how we are to behave--which some might argue are not salvific, i.e. not having any bearing on our salvation, but rather responses to the salvation we've already received--with the repeated refrain that these behaviors are part and partial to salvation. They are the actions of the redeemed, they proclaim to God and man alike the seat of our allegiance, and they are neither what saves us (only God does this) nor inconsequential to our salvation. Ezekiel 33:12-20 is not meant to scare us into having an "in again/out again" view of our salvation but, rather, a serious view of our approach to sin and wickedness. Choosing to follow God through Jesus the Christ (i.e. biblical salvation) is not a one-time prayer, followed by unconcerned wicked lifestyles, but an undeniably transformed life preceded by a moment or period of decision.
This passage makes it crystal clear that our wickedness is a big problem. It's not "inconsequential in the life of the redeemed," or "a nevertheless redeemed life sadly absent of God's blessings or eternal rewards," as some might say. Rather, I think we must go where scripture leads us and admit that we either 1) believe God's word is separated, or 2) doesn't mean what it says, or 3) our behavior is a clear and definitive sign to us and all others of our salvific relationship with God, or lack thereof. There is a difference between the sinfulness of the redeemed and the sinfulness of the lost in terms of finality. We're not talking about us being saved though our works are burned up, like Paul addresses in 1 Corinthians 3:11-15; but exhibiting the change of nature that true repentance brings (2 Corinthians 5:17, 7:1), examining ourselves in earnest (13:5) to see if we're play-acting as believers, to our destruction (11:15); or, even as we fail to live up to God's holy standards, we are aware of the nature of our sin before God and are sorrowful in our salvation (7:10). The alternatively is just being sorrowful in the worldly way, because we got caught or suffer consequences that are inconvenient to us in some way. This idea is exhibited in an old grade school question that has become popular in youth ministry, so I ask it here as a connecting point for how we can begin to examine ourselves rightly:
"If you could do anything in the world without getting in trouble, and
there were no consequences, even from God, what would you do?"