In order to understand miracles, we must first understand God's relation to His creation.
God is a living God that by one act creates and sustains the universe. If He were to forget us for one nanosecond, all things would disappear into nothingness.
A miracle is an influx of God's creative energy which, in some way, modifies the pervasive presence of the laws of nature. C.S. Lewis in Miracles states: "The divine art of miracle is not an art of suspending the pattern to which events conform but of feeding new events into the pattern".
The Incarnation is the greatest miracle of God.
"He comes down; down from the heights of absolute being into time and space, down into humanity; down further still, if embryologists are right, to recapitulate in the womb ancient and pre-human phases of life...." (C.S. Lewis). He recapitulates cosmic history since human nature is made of star-dust and He did all this in order to bring the ruined world up with Him to the Father.
The Incarnation was also a miracle from the point of view of human descent. St. Matthew traces the genealogy of Jesus from Abraham through the House of David to Joseph (Mt 1:1-17). Yet, Joseph did not generate the human nature of Christ because Mary conceived a male child by the power of the Holy Spirit. Mary gave of her humanity to the child but could not, genetically speaking, conceive a male child.
Calmed the Storm