Thanks for your question.
The miracles were for a specific purpose. They gave evidence to the authority of those who were speaking God's word. The power to perform miracles was first given to the Apostles. They were also given the ability to pass on the "Gifts of the Spirit" by the laying on of their hands (Acts 8:18). Once the Apostles died and the Word of God was completed the ability to pass on the gifts of the spirit died out too. Therefore the ability to work miracles in God's name will not be restored until the Lord Jesus returns to set up God's Kingdom. Indeed the "gifts of the spirit" were called a "taste of the powers of the age to come" in Hebrews 6:5. They were only a taste of the full power which will be given to those made immortal in God's Kingdom.
Here is a link to a document on the website dealing with this topic:
The Holy Spirit (Click the title)