The text from Hosea 5:5-6 speaks of the root cause of the downfall of Israel:
And the pride of Israel doth testify to his face: therefore shall Israel and Ephraim fall in their iniquity; Judah also shall fall with them. They shall go with their flocks and with their herds to seek the LORD; but they shall not find [him]; he hath withdrawn himself from them.
Here specifically the prophet seems to have in view worship, which had for the Israelites (and some among the Jews, as the inclusion of 'Judah also shall fall with them' in verse 5 attests, become a means of appeasing God through the mechanism of sacrifice. What bastardization of God's holy worship! What God had instituted to display his hatred of sin, and the glory of redemption in Him, the priests of Israel and Judah had variously destroyed, becoming a formal exercise. We have seen already in Hosea's prophecy the priests reprimanded and condemned for abusing worship... here, the hearts of the people are addressed more directly.
Where do we err in similar ways? I can't recount how many times I have heard people refer to Sabbath worship in ways that make me wonder whether they really do simply see what they do as what they "ought to do" rather than as a source of the ever flowing streams of living water, and a means of grace, fostering communion with the Holy God and King of all through Christ Jesus the mediator. The way sermons are complained about if they are "too long" (by whose standard??! Ezra read the Law all day!!) or when worship takes too big a chunk out of Sunday, cause me to doubt whether the complainer has a clue about the purpose, and right HEART of worship really is.
How can we work against such errors? Only by spreading God's Holy word before us and learning what HE commands in worship. Only by drinking from the fount of truth that Scripture presents us with, and learning, hearts and minds open to the Spirit's teaching, just what it is that God would have us do. Our hearts must be in a right frame, friends. The world and its concerns must be left behind, and our hearts attuned to God's praise (can you tell I've been reading Steele's 'A Remedy for Wandering Hearts in Worship'? It is amazing how God brings books in at a given moment, and how they align with Scripture that is under deep study at the same time!)
God will be pleased with us if we approach him in worship with humble hearts, and a teachable spirit. If our worship becomes formal, and our performance of it mechanical, we, like Israel, are in danger of a fall.
I'll close with some of Calvin's notes on these verses. He echoes as well some of the same notes that he played before in earlier verses discussing the heart of worship:
The Prophet here laughs to scorn the hypocrisy of the people, because they thought they had ready at hand a way of dealing with God, which was, to pacify him with their sacrifices. He therefore shows that neither the Israelites nor the Jews would gain any thing by accumulating burnt-offerings, for they could not in this way return into favor with God. He thereby intimates that God requires true repentance, and that he will not be reconciled to men, except from the heart they seek him and consecrate themselves to his service; and not because they offer brute beasts.The faithful, no doubt, expiated their sins at that time by sacrifices, but only typically: for they knew for what end and purpose God had made the law concerning sacrifices, and that was, that the sinner, being reminded by the sight of the victim, might confess himself to be worthy of eternal death, and thus flee to God's mercy and look to Christ and his sacrifice; for in him, and nowhere else, is to be found true and effectual expiation. For this end then had God instituted sacrifices: so the faithful, while offering sacrifices, did not suppose any satisfaction to be done by the external work, nor even imagined it to be the price of redemption; but they exercised themselves in these rites in faith and repentance.