Isaiah 43:10

Yahweh pointed to the people of Israel, His servant, as those who would be His witnesses that He could predict the future and bring it to pass. For example, He had promised to make Abraham a great nation, to deliver the Israelites from Egyptian bondage, to give them Canaan, and to make David’s dynasty secure. He had fulfilled all these promises and more. In the process He had made the Israelites His witnesses so they would learn that He alone is the true God (cf. Exodus 3:14). Similarly, Jesus told His disciples that they would be His witnesses (Acts 1:8). They had witnessed His works for several years and could testify to His uniqueness, even His deity. Thus the early confession of the church became "Jesus is Lord."