The literal heart must be whole to function, but the figurative heart can be divided. The psalmist, evidently a man after God’s own heart, wrote under inspiration: “The halfhearted ones I have hated.” (Psalm 119:113) Among such were those Israelites whom Elijah challenged, saying: “How long will you be limping upon two different opinions? If Jehovah is the true God, go following him; but if Baal is, go following him.” (1 Kings 18:21) Halfheartedly, they ‘limped upon two different opinions.’
Similarly, after a partial return to Jehovah by Judah, it is recorded: “Nevertheless, the people were still sacrificing upon the high places; only it was to Jehovah their God.” (2 Chronicles 33:17) With divided hearts, they claimed to worship Jehovah but in an unauthorized way and in locations where they had previously worshiped Baal. Jesus said: “No one can slave for two masters.” (Matthew 6:24) In those days slaves were like a piece of property. They were on call to their master 24 hours a day. Their time could not be divided between two masters—half for one and half for the other. Jesus was making this point: no halfhearted service to Jehovah!
There is only one literal heart in each person, but, figuratively speaking, one person can have two hearts. David referred to such persons, saying: “With a smooth lip they keep speaking even with a double heart [“with a heart and a heart,” Ref. Bi., footnote].” (Psalm 12:2) One heart posed for public display, the other secretly connived for selfish advantage. This two-faced, doublehearted posture is described in the Scriptures: “For as one that has calculated within his soul, so he is. ‘Eat and drink,’ he says to you, but his heart itself is not with you.” “Although he makes his voice gracious, do not believe in him, for there are seven detestable things in his heart.”—Proverbs 23:7; 26:25; Psalm 28:3.
Such hypocrisy in human relationships is deplorable, but when sown in Jehovah’s worship, it reaps calamity. “Do not put your trust in fallacious words, saying, ‘The temple of Jehovah, the temple of Jehovah, the temple of Jehovah they are!’ Here you are putting your trust in fallacious words—it will certainly be of no benefit at all. Can there be stealing, murdering and committing adultery and swearing falsely and making sacrificial smoke to Baal and walking after other gods whom you had not known, and must you come and stand before me in this house upon which my name has been called, and must you say, ‘We shall certainly be delivered,’ in the face of doing all these detestable things?” (Jeremiah 7:4, 8-10) Jesus denounced such doublehearted hypocrisy among the scribes and the Pharisees, saying: “You hypocrites, Isaiah aptly prophesied about you, when he said, ‘This people honors me with their lips, yet their heart is far removed from me.’”—Matthew 15:7, 8.
From all of this it is clear why Jehovah said to Samuel: “Not the way man sees is the way God sees, because mere man sees what appears to the eyes; but as for Jehovah, he sees what the heart is.” (1 Samuel 16:7) Hence, when Jehovah takes a man’s measure, it is not based on superficial evidence; he probes to the very heart of the matter. Christ Jesus identified the heart as the motivating force behind our conduct, whether it is good or bad: “A good man brings forth good out of the good treasure of his heart, but a wicked man brings forth what is wicked out of his wicked treasure; for out of the heart’s abundance his mouth speaks.” Also, “Out of the heart come wicked reasonings, murders, adulteries, fornications, thieveries, false testimonies, blasphemies.”—Luke 6:45; Matthew 15:19.
Christ Jesus, to whom judgment is committed, also looks where Jehovah looks: “I am he who searches the kidneys [“deepest emotions,” Ref. Bi., footnote] and hearts, and I will give to you individually according to your deeds.” (Revelation 2:23) For this reason, “more than all else that is to be guarded, safeguard your heart, for out of it are the sources of life.”—Proverbs 4:23.
Our worship of Jehovah must be neither halfhearted nor doublehearted, but wholehearted. This demands diligent effort on our part. Why so? Because the heart is treacherous and can be very deceptive. It is frightening how skillful it is in rationalizing the wrongs that attract our fallen flesh. While it may deceive us and hide our real motives from us, Jehovah sees it for what it is. He puts us on notice of this, saying: “The heart is more treacherous than anything else and is desperate. Who can know it? I, Jehovah, am searching the heart, examining the kidneys, even to give to each one according to his ways, according to the fruitage of his dealings.”—Jeremiah 17:9, 10.