Years ago, while playing the role of Will Parker in the musical, Oklahoma!, I sang a song called "All Er Nuthin'". In the song, Will tells his girlfriend, Ado Annie, that if she's going to love him, it has to be all or nothing. He wants to know that she will be his completely, that she will love him with all of her heart.
That is exactly how we are commanded to love our God. Jesus tells us that the greatest commandment is to love the Lord our God with all of our heart (Matthew 22:37). Not with half of our heart, but with all of it. It's all or nothing. God does not want us to be half-hearted. And that does not just apply to how we love Him.
Throughout God's Word, there are commands to do many things with all our heart. We are to seek Him or search for Him with all our heart, for it is then that we will find Him (Jeremiah 29:13). We are to trust Him with all our heart, for it is then that He will direct our paths (Proverbs 3:5-6). God requires that we serve Him, keep His commands, and walk in His ways, and He wants us to do all of these things with all our hearts (Joshua 22:5). When we praise God, it should be with all our heart (Psalm 86:12). With all our heart, we should be glad and rejoice in Him (Zephaniah 3:14).
Nothing that we do for the Lord or in His name should be done half-heartedly. When Jeroboam was king of Israel, he did not keep God's commandments with all his heart, but instead did what he felt was right. Because of Jeroboam's disobedience, God brought judgment and disaster on Jeroboam and his house (1 Kings 14:7-11). On the other hand, when Hezekiah was king of Judah, he served God, kept His commandments, and sought Him with all his heart (1 Chronicles 31:20-21). The result of this is summed up in the last sentence of verse 21 of 2 Chronicles 31: "So he prospered."
God's plan for us is to prosper (Jeremiah 29:11). As we serve and follow the Lord, as we love Him and trust Him, as walk in obedience to Him and give Him praise, we should always be sure to do so with all our heart. This is what God requires but, more importantly, it's what He deserves.