Jesus' miracles and those of the Apostles were to be as a "sign" to Israel, witnessing to the power of the Kingdom that was to come to Israel on earth. ("Thy kingdom come…on earth")

John 2:11 This beginning of miracles (Gk., semeion, signs) did Jesus in Cana of Galilee, and manifested forth his glory; and his disciples believed on him. KJV

We should note that in John 2:11, at the time of Jesus' first miracle at Cana when He turned water into wine, the word "miracle" in the KJV is not properly transliterated from the Greek. As seen in the Greek and some other Bible translations, it was the "beginning of miraculous signs".

We see in Matt 8:16 that Jesus proceeded to heal "all" the Jews that came to Him; "they brought unto him many that were possessed with devils: and he cast out the spirits with his word, and healed all that were sick…"  Jesus came as Messiah to the Jews only, since the Gentiles were as "dogs" (Matt 15:26). 

Today we see acts of God's divine mercy in healing occasionally, but not in healing "ALL" that were sick. Let's now examine why.  

All the miracles Jesus did, such as noted in John's Gospel, are to be considered signs for Israel. Paul said, "The Jews require a sign" (1Cor 1:22). From the time of John the Baptist through Jesus' life, the message they brought was that "…the kingdom of heaven is at hand" (Mat 4:17). We need to see that these miracles were "signs" to announcing and confirm to Israel the message of Messianic Kingdom being "at hand," as it had long been promised by God to Abraham's "seed."

Jesus said this of His twelve disciples. Mark 16:17 And these signs shall follow them (the Jewish Disciples) that believe; In my name shall they cast out devils; they shall speak with new tongues. This applies to "the twelve disciple" whom Jesus sent forth to preach the Messianic Kingdom of God at hand; then, as Apostles, they made the offer of the Kingdom to Israel. In the days following Pentecost, with the outpouring of the Holy Spirit "upon" the 120 of Israel; Peter, James, John and the others of the twelve Apostles did great miracles as signs. These signs confirmed the actual offer of the Kingdom to Israel, if only the nation would "repent." Of course, rather than repent, they stoned Stephen to death. Israel thereby fell and was set aside; God then turned to the Gentiles (Acts 13:46, 28:28).