There are some who say "seeing is believing" as a way to show that they are rational, scientific, or to show that they are not gullible. It seems like a safe way to approach issues of truth and fact. Often those who say this do not think any more deeply about their view of life and they fail to understand that this approach to life itself cannot be "seen". The Galileans in the text followed the Savior as long as they saw wonders and had a free meal from time to time. They admired this new popular preacher, but they were impressed merely by the outward things. Being impressed by the wisdom and power of His words, and being impressed by the novelty of His doctrine is not the same thing as trusting in Him as the only and promised Savior.
Into this crowd, a man appears. It is safe to assume that he, like the rest of the crowd, saw the wonders and heard the teaching of the Savior in Jerusalem. But he has a special need: his son was near death. What he did not yet realize is that he had a need that was even more pressing than the healing of a sick son. His desire was a desire for the Savior's power. Indeed, the Savior does have the needed power, both to heal his son and to do something much better. It is the power to save that this man really needed. But when he asked for the Savior's help he did not receive the answer he desired.
The Savior responded to the plea by scolding the crowd for their obsession with flashy signs and wonders. It is often the case that we come to the Lord with our needs (or wants) and the answer is not what we expect or want. At this point, the man still does not understand. He wanted to see the Savior come to his home and heal his son. While believing the power, he did not fully understand. Nevertheless, the Lord grants his request. What an example to us. We do not need a perfect theology in order to come to Christ and receive from Him what we need. The critical thing is what is said in verse 50, "And the man believed the word that Jesus had spoken unto him, and he went his way." That is, he had faith in spite of what his expectations were. The word of the Lord was indeed powerful in the healing of the boy. But this is not the point of the narrative.
This man testified to the great power and authority of the Savior to his household and salvation descended upon it. We do not see the mighty miracles that were performed by our Lord as that man likely did. We do not see him face-to-face as the man did here. Yet, we are called to have faith in the one who raised up the boy even though you did not witness it. Seeing is not believing. Rather, as the Scriptures say, "Whom having not seen, ye love; in whom, though now ye see him not, yet believing, ye rejoice with joy unspeakable and full of glory:" (I Peter 1:8) "So then faith cometh by hearing, and hearing by the word of God." (Rom. 10:17)