We speak truly by saying that the grass is green, but the grass is green because God spoke it to be so. If God, however, called the grass purple, the grass would be purple. While we are creatures that can only speak truth or falsehood about the creation around us, God is the Creator who shapes and fashions all things by His command.
…in hope of eternal life, which God, who never lies, promised before the ages began…
Titus 1:2 ESV
A few days ago, my eldest daughter and I had a conversation about why we can fully trust God, and as so often happens with smaller children, it was not the first time that we treat down that particular conversational path. In essence, I told her that we can trust God not only because what He says is true but because what God says is truth, that He not only never lies but He cannot lie.
But perhaps we should begin with this question: what is a lie? Or what does telling the truth mean? Well, we either speak the truth or a lie depending on how our words reflect reality. If we say something that reflects the reality around us, then those words are true, whereas if we say something that does not reflect the reality around us, then those words are false. For example, saying that the grass is blue and the sky is green is false and to do so means speaking a lie about what really is. Instead, we speak truthfully whenever we say that grass is green and the sky is blue.