Man does not change in order to be saved, but true salvation always brings about an evident change in the life of the new believer. Perhaps the change is less noticeable in some new believers and more noticeable in others; however, no change means no salvation. The change is not always an immediate outward change because it involves a change of the inward nature. A person who trusts Christ for salvation becomes a new creature (Galatians 6:15). It might be best to consider how this could be likened to a dog (Matthew 15:26-27) becoming a sheep (John 10:16). A new man now dwells within the new Christian to help combat and defeat the old sinful nature (Ephesians 4:22-24). Salvation is not merely the turning over of a new leaf; it is a new birth (John 3:3) where one is passed from spiritual death to spiritual life (John 5:24).
The Lord loves to receive sacrifices from men. Yet, it is important to recognize that the Lord looks beyond the actual sacrifices and into the heart of those making the offerings. What He sees in the heart is far more important to Him than the actual sacrifice itself. This is because a man may offer the right sacrifices but does so from a heart of ungodliness. God does not approve of such sacrifices. There were individuals who lived in the days of animal sacrifices who brought sacrifices as prescribed by the law but did so with improper motives. The Lord said of these sacrifices that to Him, these sacrifices were an abomination. Though the nature of sacrifices has changed, the fact remains that men can, and do, offer sacrifices of praise or thanksgiving outwardly all the while their hearts are far from God (Matthew 15:8).