The word translated, miracle can also mean, "sign." the Apostle John testified why he recorded Jesus' miracles.

And truly Jesus did many other signs in the presence of his disciples, which are not written in this book; but these are written that you may believe that Jesus is the Christ, the Son of God, and that believing you may have life in His name (Jhn 20:30-31).

The Miracles Testified to Jesus' Identity

The miracles were done as a testimony to the identity of Jesus which would create belief in Him. These signs that Jesus performed convinced many that He was the Messiah.

Now when he was in Jerusalem at the Passover, during the feast, many believed in his name when they saw the signs which he did (Jhn 2:23).

Some Doubted the Miracles

Yet even with all these miraculous signs, there were some who doubted. When Jesus was speaking to the multitude, He said:

'Father, glorify your name.' Then a voice came from heaven saying, 'I have both glorified it and will glorify it again.' Therefore the people who stood by and heard it said that it had thundered. Others said, 'An angel has spoken to him' (Jhn 12:28-29).

Though it was the voice of the Father who spoke, many believed they only heard thunder.

After Jesus' resurrection there were still some who did not believe.

And when they saw him, they worshipped him, but some doubted (Mat 28:17).

Consequently the evidence of Jesus' miracles did not cause everyone to believe. There were still people who rejected Him.

Summary

The miracles of Jesus were performed as signs to testify to his unique identity. And although the signs convinced many, there were still some who doubted.