'My Covenant' in the Bible

For thus said Jehovah of the eunuchs, Who do keep My sabbaths, And have fixed on that which I desired, And are keeping hold on My covenant:

And sons of the stranger, who are joined to Jehovah, To serve Him, and to love the name of Jehovah, To be to Him for servants, Every keeper of the sabbath from polluting it, And those keeping hold on My covenant.

And I -- this is My covenant with them, said Jehovah, My Spirit that is on thee, And My words that I have put in thy mouth, Depart not from thy mouth, And from the mouth of thy seed, And from the mouth of thy seed's seed, said Jehovah, From henceforth unto the age!