“Cursed is the cheat who promises to give a fine ram from his flock but then sacrifices a defective one to the Lord.” Malachi 1:14a NLT

Successful athletes sacrifice much in striving to achieve the best they can be. When reaching the pinnacle of being able to perform at a high level, they do not slack off, but continue to give their best. Their desire is to see the results of heavy training, a healthy diet, and the sacrificing of creature comforts. Giving their best is self-satisfying and pleasing to teammates in a team sport. When one does not give their best in the sporting world it is very noticeable. Teammates and fans alike recognize it immediately and one’s individual statistics cannot hide the fact. Giving a lackluster performance when one is more than capable to step it up by giving their best is, well let’s say, cheating.
God accused Israel of cheating by not giving their best sacrifice. They had it in their power to do so, they had their best, and even promised to do so, but chose to not give it. God demanded the very best, an unblemished animal, for sacrifice. Israel thought they would get by offering a less than stellar performance but they did not get away with it.
Christians today will also not get away with not giving their best in serving the Lord. God is holy and He demands the best that each one of us is capable of doing. He will call us out. We cannot hide or get away with it. The talents and gifts the Lord has given to us are to be used for His honor and His glory to the best of our ability. Although I am a sports enthusiast I was never much of an athlete, but the Lord has given me other talents that I am to use in serving Him. All of us have the opportunity and capability, with the Lord’s help, to give our best. Give your best to the Lord!
Read the account of Israel giving unworthy sacrifices: https://www.biblegateway.com/passage/?search=Malachi+1%3A6-14&version=NLT