"And he said, The things which are impossible with men are possible with God" (Luke 18:27).
A good definition of a miracle is "an event which is impossible scientifically, but which happens anyway." Modern scientism often rejects the concept of special creation, because it requires the supernatural work of a Creator. But that is the very point! This world and its complex systems could never have arisen by "natural" processes.
The specific context of this key verse, however, is the great work of salvation. The Lord Jesus had just shocked a rich and morally upright young ruler by telling him that, to inherit eternal life, he needed to give all his possessions to the poor, thus laying up treasure in heaven. This he would not do, and so Jesus said, "How hardly shall they that have riches enter into the kingdom of God! For it is easier for a camel to go through a needle's eye, than for a rich man to enter into the kingdom of God" (Luke 18:24-25). The astonished disciples, who had always thought that wealth was a mark of God's favor, exclaimed, "Who then can be saved?" (v.26). Jesus then answered, in the thrilling words of our text.
Salvation requires a miracle--a miracle of special creation (II Corinthians 5:17). The rich man must become a different man altogether--a poor man in fact, no longer "trust-|ing| in riches" (Mark 10:24), but only in Him. "Come, take up the cross, and follow me," He told the rich young ruler (Mark 10:21). This does not necessarily mean that a rich man must actually give all his possessions away, but it does mean he can no longer trust in his riches (or any attribute, skill, etc.), or use them merely for his own selfish pleasure.
When a person really yields his life to Christ for salvation, therefore, the God of the impossible supernaturally makes him into a new creation, and his wealth, and strength, and talents, as well as his very life, all belong to his new Lord. HMM