The simple answer to that question is that I understand that "all" means "all". But if that does not satisfy you, lets dig a bit deeper. If we go to the 56th chapter of the book of the prophet Isaiah, we will read that proclamation in the following context.
1 Thus says the Lord: Maintain justice, and do what is right, for soon my salvation will come, and my deliverance be revealed.
2 Happy is the mortal who does this, the one who holds it fast, who keeps the sabbath, not profaning it, and refrains from
doing any evil.
3 Do not let the foreigner joined to the Lord say, "The Lord will surely separate me from his people"; and do not let the
eunuch say, "I am just a dry tree." 4 For thus says the Lord: To the eunuchs who keep my sabbaths, who choose the things
that please me and hold fast my covenant, 5 I will give, in my house and within my walls, a monument and a name better
than sons and daughters; I will give them an everlasting name that shall not be cut off. 6 And the foreigners who join
themselves to the Lord, to minister to him, to love the name of the Lord, and to be his servants, all who keep the sabbath,
and do not profane it, and hold fast my covenant— 7 these I will bring to my holy mountain, and make them joyful in my
house of prayer; their burnt offerings and their sacrifices will be accepted on my altar; for my house shall be called a house
of prayer for all peoples.