Revelation 19:10 says, “For the testimony of Jesus is the spirit of prophecy.”  Testimonies are what create the atmosphere for God to repeat the miracle. Testimony in Hebrew means “to do again.” The reason there is so much power in them is because it’s releasing what God has already done and setting Him up to do it again. Who doesn’t want to see a miracle repeated?

Pasted from <https://www.in-due-time.com/faith/the-power-of-testimonies/>

From merriam-webster.com

Testimony:

1 a : a solemn declaration usually made orally by a witness under oath in response to interrogation by a lawyer or authorized public official

b : firsthand authentication of a fact : evidence

c : an outward sign

2 a : an open acknowledgment

b : a public profession of religious experience

3 a(1) : the tablets inscribed with the Mosaic law

(2) : the ark containing the tablets

b : a divine decree attested in the Scriptures

From Study Bible

With a variety of meaning in Scripture, testimony, depending upon the context, denotes (1) witness, (2) evidence which witnesses to or for something,…