This woman had "heard about Jesus" (Mark 5:27). Her faith was based on hearing rather than on sight (cf. II Cor. 5:7). "She came behind Him in the crowd and touched His garment." The nature of her affliction made her unclean according to Leviticus 15:25. Her consciousness of this fact is likely what caused her to timidly approach Jesus from behind. She wanted to avoid being noticed.
She believed that if she could touch the "hem of His garment" (Matt. 9:20) she would be healed. She didn't feel a need to bother Him. Her intent was to merely touch His clothing and move on. Such a strong faith is what caused her to take action.
As she touched the hem of Jesus' garment, she was healed instantly of the affliction that had plagued her for years! Immediately, the Lord turned around and asked - "Who touched My clothes?" (Mark 5:30). He asked this question because He knew that "power had gone out of Him." Some have wondered whether Jesus consciously healed this woman or not. In other words, did He have knowledge of the miracle other than the sensation of power leaving Him? It seems unreasonable to conclude that such a healing power would go forth from Him without the full knowledge and consent of His will. Certainly He must have known this woman was approaching Him and He allowed the power to go forth and heal her. Thus, the question He asked here was not to obtain information (cf. John 2:25). He asked the question so the woman might herself make a confession of the entire matter, by which the power of her faith and the greatness of the miracle might be made known to the praise of God.
According to Luke 8:45, Peter, the disciple known for his impulsiveness, spoke up because he couldn't believe that Jesus would ask who touched Him. He thought such an inquiry was absurd since many people pressed about Jesus tightly.
Let it be observed that there is a difference between mere contact and a believing touch. Surely it is the case that others in the crowd had made contact with Jesus' garments as they walked to Jairus' house. But, no power to bless or heal went forth from Him on those instances. It was only the touch of faith that could draw this sort of miraculous blessing and transform a life. Today, a casual contact with Jesus is not enough to heal one spiritually. We, like this woman, must have a faith that leads us to act without doubting. Although we cannot touch Jesus' garments today to be healed, we can (and must) submit to Him in obedience. If we do this, spiritual healing (i.e., forgiveness of sins) is certain (cf. Heb. 5:8,9).
The healed woman's joy was suddenly turned to fear. Perhaps she was worried because of the fact that she was unclean and had touched Him. Perhaps she expected a severe rebuke for her actions. Perhaps she regretted the means she had employed to be healed.
In spite of her fear and trembling, she didn't run away as a thief would but took responsibility for her actions. She "fell down before Him and told Him the whole truth." According to Luke, she publicly acknowledged what she had done, why she did it, and the blessing she had received (Luke 8:47). If Jesus had allowed this woman to depart without this exposure, she would have mistakenly believed that Jesus healed by His nature rather than by His will (and an opportunity to bring glory to God would have been neglected).
Jesus did not rebuke her as she might have expected. Her faith received a sweet welcome from Him. Jesus stated that her faith had made her well. Her faith was not the actual source of healing, but it brought her into contact with Jesus who had the power to heal. She most likely would have died with this affliction had she not been motivated to act by faith. In like manner, today it is not enough to merely have a mental belief in Jesus. If one's faith does not motivate one to actions of obedience, then such a faith is dead and worthless (cf. James 2:26; John 14:15).