A prominent feature of the Old Testament was the repeated offering of animal sacrifices. These were, in effect, object lessons and symbols given to highlight truths God wanted remembered as Israel worshipped Him. The prophet Hosea notes that they were very active in going through these forms of worship. They were "profound to make slaughter".
The outward ordinances of worship are good in their place. They are intended to be an acting out of certain truths believed and serve as a reminder and testimony of spiritual truth. The animal sacrifices signified that the worshipper recognized he had sins that needed to be atoned for and that God would one day provide a sacrifice which could take away those sins. From our perspective today, we know that this provision has been fulfilled in the death of Jesus Christ, God's Son on the cross.
However, the people in Hosea's day were living wicked lives that God had to be "a rebuker of" - while they religiously carried on the appointed rounds of Moses' law.. Hosea makes many references to their strange attempts to blend together a life of sin and the worship of the Lord. The people fastidiously brought the animals needed for the offerings, but had no exercise of heart about their sin to go with it. "They shall go with their flocks and with their herds to seek the LORD; but they shall not find him; he hath withdrawn himself from them" (Hosea 5:6). To put it into today's terms - they went to church, but God wasn't there.
Hosea went on to write, "They sacrifice flesh for the sacrifices of mine offerings, and eat it; but the LORD accepteth them not" (Hosea 8:13a). This is a mirror of the way things are today in much that calls itself Christian. The apostles told us that this would take place. "Having a form of godliness, but denying the power thereof: from such turn away" (II Timothy 3:5). The forms of Christianity are all about us, but they are often part of a larger program that denies the power of Jesus Christ to change sinful lives.