And he believed, and his whole house. It may appear absurd that the Evangelist should mention this as the commencement of faith in that man, whose faith he has already commended. Nor can it be supposed that the word believe -- at least in this passage -- relates to the progress of faith. But it must be understood that this man, being a Jew and educated in the doctrine of the Law, had already obtained some taste of faith when he came to Christ; and that he afterwards believed in the saying of Christ was a particular faith, which extended no farther than to expect the life of his son. But now he began to believe in a different manner; that is, because, embracing the doctrine of Christ, he openly professed to be one of his disciples. Thus not only does he now believe that his son will be cured through the kindness of Christ, but he acknowledges Christ to be the Son of God, and makes a profession of faith in his Gospel. His whole family joins him, which was an evidence of the miracle; nor can it be doubted that he did his utmost to bring others along with him to embrace the Christian religion.

Himself believed - This miracle removed all his doubts, and he became a real disciple and friend of Jesus.
His whole house - His whole family. We may learn from this,
1. That sickness or any deep affliction is often the means of great good. Here the sickness of the son resulted in the faith of all the family. God often takes away earthly blessings that he may impart rich spiritual mercies.
2. The father of a family may be the means of the salvation of his children. Here the effort of a parent resulted in their conversion to Christ.
3. There is great beauty and propriety when sickness thus results in piety. For that it is sent. God does not willingly grieve or afflict the children of men; and when afflictions thus terminate, it will be cause of eternal joy, of ceaseless praise.
4. There is a special charm when piety thus comes into the families of the rich. and the noble. It is so unusual: their example and influence go so far; it overcomes so many temptations, and affords opportunities of doing so much good, that there is no wonder that the evangelist selected this instance as one of the effects of the power and of the preaching of the Lord Jesus Christ.

So the father knew - He had the fullest proof that his son's cure was supernatural, and that it was wrought by the Lord Jesus.
Himself believed, and his whole house - He and his whole family became true converts to the doctrine of the manifested Messiah. The whole family, impressed with the great kindness of God in sending health to the child, were the more easily led to believe in the Lord Jesus. The sickness of the child became the mean of salvation to all the household. They, no doubt, thought at first that God was dealing hardly with them, when threatening to remove the child; but now they see that in very faithfulness God had afflicted them. Let us learn never to murmur against God, or think that he does not act kindly towards us. His wisdom cannot permit him to err; his goodness will not suffer him to do any thing to his creatures but what may be subservient to their best interests. By providential occurrences, apparently the most adverse, he may be securing our eternal salvation.
There is an account in Beracoth, fol. 34, very similar to this of the evangelist, and very possibly stolen from this holy source. "When the son of Rab. Gamaliel fell sick, he sent two of his disciples to R. Chanina, that he would pray to God for him. When he had seen them, he went on the roof of his house and prayed for him. He then came down and said to them, His fever has departed from him. They said unto him, Art thou a prophet? He answered, I am neither a prophet, nor the son of a prophet; but when I can recite my prayers readily, I know I shall be heard. They then wrote down the hour; and, when they returned to R. Gamaliel, he said to them, Ye have fulfilled your ministry - in respect to my son, all is complete. In that hour the fever (חמה chomah, ὁ πυρετος) left him, and he desired water to drink." Schoettgen very properly remarks, Ovum ovo non magis simile est, atque haec fabula narrationi evangelicae. "One egg is not more like to another, than this fable to the evangelical narration."

So the father knew that it was at the same hour,.... Precisely;
in that which Jesus said to him, thy son liveth: he had observed what time of day it was, in which he conversed with Jesus; and particularly, when he told him his son was alive and well, and when he took his leave of him; and by comparing the account of his servants, with that, found that things entirely agreed, and that the cure was wrought exactly at the time, that Jesus spoke the words:
and himself believed, and his whole house; when he came home, he related the whole affair to his family, and he and they all believed, that Jesus was the Messiah, and became his disciples and followers: if this nobleman was Chuza, Herod's steward, we have an account of his wife, whose name was Joanna, that she followed Christ, and ministered to him of her substance, with other women, Luke 8:3. There is a story, told by the Jews, and which seems somewhat like to this (d);
"it is reported concerning R. Chanina ben Dosa, that when he prayed for the sick, he used to say, , "this liveth", and this dies; it was said to him, whence knowest thou this? he replied, if my prayer be ready in my mouth, I know that he is accepted (of God, i.e. the sick man for whom he prayed); but if not, I know that he will be snatched away (by the disease):''
upon which the Gemarists give the following relation (e);
"it happened that the son of Rabban Gamaliel (the Apostle Paul's master) was sick, he sent two disciples to R. Chanina ben Dosa, to ask mercy for him; when he saw them, he went up to a chamber, and sought mercy for him; and when he came down, he said unto them, , "go your way, for the fever has left him"; they said unto him, art thou a prophet? he replied, I am not a prophet, nor the son of a prophet; but so I have received, that if my prayer is ready in my mouth, I know that he is accepted; and if not, I know that he shall be snatched away; and they sat and wrote and observed "the very hour"; and when they came to Rabban Gamaliel, he said unto them, this service ye have not been wanting in, nor abounded in; but so the thing was, that in that hour the fever left him, and he asked of us water to drink.''
Which story perhaps is told, to vie with this miracle of Christ, and to obscure the glory of it.
(d) Misn. Beracot, c. 5. sect. 5. (e) T. Bab. Beracot, fol. 34. 2.