AN UNDIVIDED HEART
The heart of a Christian should not be divided. God has given you two eyes, that you may look both above and beneath you; that you may contemplate both heaven and hell. He has given you two ears, that you may hearken both to the accuser and the accused, when you have to judge between them. He has give you two hands, that you may raise one upwards to God, and receive, and stretch forth the other towards your neighbour, and give; two feet, that you may serve yourself and your master. But God has given you only one head and one heart.
God Approves Not of the Double-minded
God does not approves of those who are double-minded, or double-tongued; from whose lips comes forth at the same time that which is cold and hot. He does not approve of those who speak not the same when they sit as when they stand and who divide their heart between Him and the devil. A double-hearted man is a monster, which God will not accept as an offering. God demands an undivided heart.
Satan Demands an Undivided Heart
Such, also, is the demand of Satan; for though he may not immediately persuade you that you should give him your heart, and seems to be satisfied with a part of it, yet he aims at the whole. He knows full well that God will not receive a divided heart, and that therefore the whole shall yet be his own, being rejected of God.
The heart is but of small capacity; but if it were greater, it would be your duty to make it the undivided dwelling-place of Him from whom you have received it, and who alone can make it better. Who has given you authority to dispose of that which was not yours, but God’s? To Him the whole belongs, and not merely a portion. How is it possible that you can unite God and Satan within you? How can they both take a part of one heart?
Blessed are the Pure in Heart
Satan tempts to that which is evil; God moves you to that which is good. God destroys the work of Satan; Satan, on the other hand, would throw down the work of God. Where God dwells is heaven, where Satan dwells is hell. How can your heart, at the same time, be in heaven and in hell? Where God dwells, he is served and obeyed; where Satan dwells, he also is obeyed. Can you serve two masters so opposite in every respect?
God has given me my whole heart, not to use it at its uncontrolled possessor, but as a steward, answerable to Him. I will, by his grace, not abuse my trust; but restore him his own. My heart is His, not mine!
(Lutheran devotional published in 1799)