For Herod feared John - That is, he stood in awe of him on account of his sanctity, and his boldness and fearlessness in reproving sin.
Knowing that he was a just man and an Holy - A holy, pious, upright, honest man - a man who would not be afraid of him, or afraid to speak his real sentiments.
And observed him - Margin, "kept him, or saved him." This does not mean that he "observed" or obeyed his teachings, but that he kept him in safe custody in order to preserve him from the machinations of Herodias. He was willing to show his respect for John, and to secure him from danger, and even to do "many things" which might indicate respect for him - at least, to do so much as to guard him from his enemies.
And did many things - But he did not do the thing which was demanded of him - to break off from his sins. He attempted to make a compromise with his conscience. He still loved his sins, and did "other" things which he supposed might be accepted in the place of putting away, as he ought, the wife of his brother - the polluted and adulterous woman with whom he lived. Perhaps he treated John kindly, or spoke well of him, or aided him in his wants, and attempted in this way to silence his rebukes and destroy his faithfulness. This was probably before John was imprisoned. So sinners often treat ministers kindly, and do much to make them comfortable, and hear them gladly, while they are still unwilling to do the thing which is demanded of them - to repent and believe the gospel. They expect that their kind attentions will be accepted in the place of what God demands - repentance and the forsaking of their sins.

For Herod feared John, knowing that he was a just man and an holy, and observed him; and when he heard him, he did many things, and heard him (n) gladly.
(n) The tyrant was very well content to hear sentence pronounced against himself, but the seed fell upon stony places.

For Herod feared John,.... Had him in great respect; he had a great veneration for him; which was the reason that Herodias could not as yet accomplish her design against him, and vent her rage upon him. Though some understand this not of his reverence, but of his dread of him: he knew as follows, that he was a man exemplary for justice and holiness, which gained him great esteem among the people; wherefore, though Herod, as well as Herodias, could very willingly have put him to death, yet, as Matthew says, "he feared the multitude", Matthew 14:5, who, in general, had an high opinion of John as a prophet, and a holy good man: he feared therefore to take away his life, lest they should rise and rebel against him; nor would he suffer Herodias to do it, for the same reason.
Knowing that he was a just man, and an holy; by what he had heard of him, by his own conversation with him, and the observation he had made upon his tenets and conduct. He was a "just", or "righteous" man, in a civil, legal, and evangelical sense: he did that which was just, between man and man; he did to others, as he would be done by himself; he was outwardly righteous before men, he lived soberly and righteously; nor was he chargeable with any notorious breach of the law; his conversation was strictly moral: and he was just or righteous before God, through the righteousness of Christ imputed to him; in whom he believed, and to whom he looked as the Lamb of God, that taketh away the sin of the world: but it was in the former sense, that he was known by Herod to be a just man; who only could pass such a judgment upon him, by his outward conduct and manner of life: and so as he had true principles of internal holiness wrought in him by the Spirit of God, with which he was filled from his mother's womb; he was externally holy in his walk and conversation, which was visible to others, and was taken notice of by this wicked prince: the former of these characters may regard his justice, uprightness, and integrity among men; the latter, his piety and devotion unto God: and the whole agrees with the account the Jewish historian (z) gives of him, that he was
"an excellent good man, who stirred up the Jews to the study of virtue, and especially piety and justice.''
These were epithets, which used to be given to men, famous for religion and piety; so we read of Simeon, "the just" (a), and of R. Simeon, "the Holy One" (b):
and observed him: or "kept him" in custody, in prison, as the Vulgate Latin, Syriac, and Ethiopic render it; and did not put him to death, but preserved him from the designs of Herodias against him. Or he observed and took notice of what he had heard him say in his ministry; he laid it up, and kept it in his mind, and memory; the remembrance of which kept him in awe, and he durst not, and could not for the present, give heed to the solicitations of Herodias, or suffer her to take away his life: and he also observed his exemplary life and conversation, which was so just and upright, that his conscience would not admit him to give him up to her will and pleasure.
And when he heard him, he did many things, and heard him gladly: when he heard John explain the law and the prophets, open the writings of the Old Testament, preach the doctrine of repentance towards God, and faith in the Messiah to come; set forth the evil, danger, and punishment of sin, and exhorted to a holy life and conversation; taught the doctrine of baptism for the remission of sin by Christ, and spoke of the glories and happiness of a future state, and of the nature of the Gospel dispensation, just now ushering in; Herod, like one of the stony ground hearers, received the word with joy, was pleased with it, and in some things outwardly reformed: but the word did not take root in his heart, and therefore what external effects it produced, came to nothing; nor was he able to withstand the lusts and corruptions of his heart. The sense seems to be, that while he was hearing John, his natural affections were moved, and he had a kind of pleasure in the things he delivered; just as the Jews for a season rejoiced in his light, John 5:35, his natural conscience dictating to him, that the things which were spoken, were right, and just, and good; and they were delivered in such a solemn and striking manner, as commanded attention and awe; and were things of such a nature and importance, that from a principle of self-love, he could not but wish himself an interest in: and so far they had such an influence upon him, as to engage him to do many things in an external way, which had the appearance of good, at least of moral good: so that it is manifest from hence, that persons may have a natural affection for the ministry of the word, and seem delighted with it for a while; yea, may do a great many good actions, which seem to be such; and yet the word come in word only, and not in power: there may be all this, and yet true grace may not be wrought, and the word not be the engrafted word, which is able to save. In one of Beza's copies, and so in one of Stephens's, and in the Coptic version, instead of "he did many things", it is read, "he hesitated much": he was perplexed and distressed, he did not know what to do with himself; his conscience was uneasy, some things were pleasing to him, and others greatly afflicted him; his mind was distracted, he could not tell what to think, say, or do: however, it had such an effect upon him, that he had some respect for John; a veneration of him; at least, some fear and dread of him, which kept him from taking away his life, or suffering any others to do it.
(z) Joseph. Antiqu. l. 18. c. 7. (a) Pirke Abot, c. 1. sect. 9. (b) T. Bab. Succah, fol. 52. 2.

For Herod feared John--but, as BENGEL notes, John feared not Herod.
knowing that he was a just man and an holy--Compare the ease of Elijah with Ahab, after the murder of Naboth (1-Kings 21:20).
and observed him--rather, as in the Margin, "kept" or "saved him"; that is, from the wicked designs of Herodias, who had been watching for some pretext to get Herod entangled and committed to despatch him.
and when he heard him, he did many things--many good things under the influence of the Baptist on his conscience.
and heard him gladly--a striking statement this, for which we are indebted to our graphic Evangelist alone, illustrating the working of contrary principles in the slaves of passion. But this only shows how far Herodias must have wrought upon him, as Jezebel upon Ahab, that he should at length agree to what his awakened conscience kept him long from executing.

Herod feared John. Was in awe of him as a holy man, and feared the indignation of the people if he slew him.

And preserved him - Against all the malice and contrivances of Herodias. And when he heard him - Probably sending for him, at times, during his imprisonment, which continued a year and a half. He heard him gladly - Delusive joy! While Herodias lay in his bosom.