What does it mean that it is impossible for God to lie (Hebrews 6:18)?

Answer

Hebrews 6:18 elaborates on previous verses by stating, “So God has given both his promise and his oath. These two things are unchangeable because it is impossible for God to lie. Therefore, we who have sought refuge in him can have great confidence as we cling to the hope set before us” (NLT). The broader context of this discussion centers on God’s promises, as demonstrated through Abraham. Verse 13 emphasizes how God confirmed His promise to Abraham by making an oath in His own name, doing so to “make the unchanging nature of His purpose very clear.” We can rely on His promises because of His faithfulness. God cannot deceive.
God’s truthfulness is linked to His holiness, a characteristic of His absolute moral perfection. His holiness also encompasses integrity, described as “unwavering adherence to moral principles.” Nevertheless, God does not conform to any moral standard; He is the ultimate standard. Because of God’s complete goodness and total separation from all types of evil (including falsehood), we trust that His Word is true (see John 17:17).
The entire epistle to the Hebrews seeks to warn, challenge, and encourage persecuted believers, especially Jewish converts who may have been tempted to renounce their faith. Hebrews 6:18 provides encouragement, as it is God’s unwavering truthfulness and unchangeableness that provide hope. This hope is referred to as “an anchor for the soul, firm and secure” (verse 19). If God were to deceive us about His work through Jesus, we would have no hope, no anchor. Therefore, our trust in God is based on His immutable nature.
Faith is only as reliable as its object. As Timothy Keller emphasized, “It is not the strength of your faith but the object of your faith that actually saves you. Strong faith in a weak branch is fatally inferior to weak faith in a strong branch” (The Reason for God, Penguin Books, 2009, p. 244). We can place our faith in God.

Because it is impossible for Him to lie.

Consider two aircraft, one in good mechanical condition, and the other with a faulty engine. A person will reach his or her destination in the reliable aircraft regardless of the amount of faith he or she has. Even weak faith in the reliable plane is enough to reach the destination safely. Conversely, even strong faith in the faulty craft will not compensate for the plane’s broken condition. It’s not the faith that gets us to our destination, but the vehicle we are in. So it is with our salvation. It’s not the strength of our faith that saves us but the strength of our Savior. He is the Truth «Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me. », (John 14:6), and it is impossible for Him to lie.

Several other passages affirm God’s immutability and truthfulness. An example is Numbers 23:19, “God is not human, that he should lie, not a human being, that he should change his mind. Does he speak and then not act? Does he promise and not fulfill?” The apostle James also asserts that God “does not change like shifting shadows” «Every good gift and every perfect gift is from above, and cometh down from the Father of lights, with whom is no variableness, neither shadow of turning. », (James 1:17).

Because it is impossible for God to lie, we can have confidence in the gospel message. We know that, when God declares us forgiven and righteous, He can be trusted. We are welcomed into His kingdom and reconciled to Him because His word is absolute. This confidence permeates our lifestyle, motivating us to live for God. It also produces hope within us and resilience in the face of adversity. In moments of doubt, it is a valuable practice to reflect on God’s unchanging attributes, as revealed in Scripture.