Why does Jesus say that his words in this letter come from "the true one"?

Revelation 3:7 (ESV)

7 “And to the angel of the church in Philadelphia write: ‘The words of the holy one, the true one, who has the key of David, who opens and no one will shut, who shuts and no one opens.

The term appears repeatedly in the Old Testament as descriptive of God’s identity and works (see Exodus 34:6; Psalm 86:15; Isaiah 65:16). He is “true” because his words always translate into deeds, and so he is known as reliable, faithful, true. This truthfulness reveals his holiness, his otherness, for there is none like him whose works always line up with his words. Though the two terms in this verse, holy one and true one, are used of God in the Old Testament, Jesus does not hesitate to apply them to himself in his self-description to Philadelphia. With these terms Jesus makes clear that he will most certainly keep the promises contained later in this letter.