Biblically, the human heart is the place of the emotions, the intellect, and the will. It is the place where we think, feel, and make decisions. It is the most inner part of our being.
When we say that God desires service that flows from the heart, we mean that God wants more from us that just outward conformity to a set of rules, a schedule, or a task list. It means that we serve with with desire that flows from the inner most part of our being.
There are many passages that bear this out. When Moses was taking an offering for the construction of the Tabernacle, God gave him these instructions, "The Lord said to Moses, “Speak to the people of Israel, that they take for me a contribution. From every man whose heart moves him you shall receive the contribution for me." (Ex 25:1–2 ESV) In the New Testament, Paul wrote, "Whatever you do, work heartily, as for the Lord and not for men," (Col 3:23 ESV)
The Lord Jesus Christ made this indictment of the religious crowd of His day, "‘This people honors me with their lips, but their heart is far from me;'" (Matt 15:8 ESV) They went through all of their rituals. They knew the right words to day. But their hearts weren't in it.
It is very easy to fall into outward conformity to spiritual activities, and yet be far from God in our hearts. We can go through the motions of reading our Bibles, praying, attending church, and even serving in some ministry, and yet have little affection and passion in our hearts for what we are doing, and for the God for Whom we are doing it. This can only be a temporary condition, because as human beings we will not do for long that which brings us little or no joy.
Some have concluded the answer is just to stop the spiritual activities until their heart changes. The problem with that reasoning is that the very activities that have become perfunctory, are often the means of grace that God uses to change the heart.
The psalmist shows us that crying out to God to change our heart is what is needed. He prayed things like: "Let the words of my mouth and the meditation of my heart be acceptable in your sight, O Lord, my rock and my redeemer." (Psa 19:14 ESV) and "Create in me a clean heart, O God, and renew a right spirit within me." (Psa 51:10 ESV) "Teach me your way, O Lord, that I may walk in your truth; unite my heart to fear your name." (Psa 86:11 ESV) "Incline my heart to your testimonies, and not to selfish gain!" (Psa 119:36 ESV). The psalmist prayed for the condition of his own heart!
We too need the gracious intervention of our God, to change the condition of our own hearts from time to time. If you find that your heart has become cold, and you are lacking the passion and the joy that you once had, cry out to your Father, confess and ask Him to help you! He is gracious, kind, and He will!
In Genesis 13:16 we find these words spoken by God to Abraham, "for all the land that you see I will give to you and to your offspring forever. I will make your offspring as the dust of the earth, so that if one can count the dust of the earth, your offspring also can be counted." (Gen 13:15–16 ESV) At the moment God spoke these words, Abraham was a nomad who owned no land. He had no children, and was married to a barren woman. Everything that God promised him was at that moment absent from His life. It would be several years before Abraham would receive even a partial fulfillment of these promises. But his present condition was not his final condition!
Two chapters later, God again appears to Abraham, and says these words: Fear not, Abram, I am your shield; your reward shall be very great.” (Gen 15:1 ESV) to which Abraham responds: “O Lord God, what will you give me, for I continue childless, and the heir of my house is Eliezer of Damascus?” And Abram said, “Behold, you have given me no offspring, and a member of my household will be my heir.”" (Gen 15:2–3 ESV) Abraham is still in the same condition that he was when God promised to make his offspring as the dust of the earth—childless! But His present condition is not his final condition! God reiterates His promise, "And behold, the word of the Lord came to him: “This man shall not be your heir; your very own son shall be your heir.” And he brought him outside and said, “Look toward heaven, and number the stars, if you are able to number them.” Then he said to him, “So shall your offspring be.”" (Gen 15:4–5 ESV) This time the scripture adds, "And he believed the Lord, and he counted it to him as righteousness." (Gen 15:6 ESV)
We all know the story. When Abraham and Sarah were well beyond the age of childbearing, God began to fulfill His promise by giving Abraham, a son. He went from being childless to becoming the father of many nations! His present condition had not been his final condition!
Sometimes it seems as though our lives are not making the impact that we really want them to make. We feel barren and unproductive. But God has made some promises to us, upon which we can rest, promises like—“Therefore, my beloved brethren, be ye stedfast, unmoveable, always abounding in the work of the Lord, forasmuch as ye know that your labour is not in vain in the Lord." (1 Cor 15:58 KJV) and "And let us not be weary in well doing: for in due season we shall reap, if we faint not." (Gal 6:9 KJV)
Whatever condition you may be facing right now that may be bringing you grief, find a promise of God that applies, trust it, and realize that your present condition is not going to be your final condition! Then patiently wait for God’s timing.