The first angle I'm going to work from is that that the ethics of creatures proceed from their Creator.
So, who is our Creator?
God is not a man,a that he should lie... (Num 23:19 NIV)
He who is the Glory of Israel does not lie (1Sa 15:29 NIV)
God, who does not lie... (Tit 1:2 NIV)
...him who is holy and true... (Rev 3:7 NIV)
Just and true are your ways, King of the ages. (Rev 15:3 NIV)
... is called Faithful and True. (Rev 19:11 NIV)But do we need to try and be like God in this respect? Or is truth an 'incommunicable' attribute of God? One that He possesses, but we're not commanded to emulate? Well, Colossians specifically combines the command not to lie with the destiny of the believer to be like his/her Creator:
Do not lie to each other,a since you have taken off your old self with its practices and have put on the new self, which is being renewed in knowledge in the image of its Creator. (Col 3:9-10 NIV)This is not only our future, but also the expectation of the character of our lives now:
Yet a time is coming and has now come when the true worshippers will worship the Father in spirit and truth, for they are the kind of worshippers the Father seeks. 24 God is spirit,a and his worshippers must worship in spirit and in truth." (Joh 4:23-24 NIV)And this in anticipation of our future. As John sees in Revelation:
Then I looked, and there before me was the Lamb, standing on Mount Zion, and with him 144,000 who had his name and his Father's name written on their foreheads. ... No lie was found in their mouths; they are blameless. (Rev 14:1-5 NIV)So while we may not necessarily act truthfully instinctively, honesty is the direction the Christian must be pointed towards because it's what conforming to the image of his/her Creator looks like.
Our ethics flow from the nature of our Creator.