Salvation for all?

Is there a plan for salvation for gentiles in the OT... without Jesus?

Isaiah 56:3-8 --

Let no foreigner who has bound himself to the LORD say, "The LORD will surely exclude me from his people." And let not any eunuch complain, "I am only a dry tree."

4 For this is what the LORD says: "To the eunuchs who keep my Sabbaths, who choose what pleases me and hold fast to my covenant-

5 to them I will give within my temple and its walls a memorial and a name better than sons and daughters; I will give them an everlasting name that will not be cut off.

6 And foreigners who bind themselves to the LORD to serve him, to love the name of the LORD, and to worship him, all who keep the Sabbath without desecrating it and who hold fast to my covenant-

7 these I will bring to my holy mountain and give them joy in my house of prayer. Their burnt offerings and sacrifices will be accepted on my altar; for my house will be called a house of prayer for all nations."

8 The Sovereign LORD declares— he who gathers the exiles of Israel: "I will gather still others to them besides those already gathered."


Despite the OT being basically about Israel and how God chose them to save, here we see that God has also included the gentiles for salvation. And all without sending Jesus. The sole stipulation is that these foreignors keep God's sabbaths holy and keep from evil, two things Christians can't seem to do.

Where in the OT does God indicate that he is planning to send his only son to die for the sins of mankind?

Can someone point me to the passage where God indicates that he is going to come to Earth himself as a human being?

If his plan all along was to send Jesus then why all this nonsense about giving salvation to anyone and everyone who worships him and offers sacrifices on his holy mountain?

Why are keeping his sabbaths so important to him if he knew he was just going to superseded all that by sending Jesus?