The commandment of truthfulness is really only another name for the totality of discipleship. Only those who follow Jesus and cleave to him are living in complete truthfulness. Such men have nothing to hide from their Lord. Their life is revealed before him, Jesus has recognized them and led them into the way of truth. They cannot hide their sinfulness from Jesus, for they have not revealed themselves to Jesus, but he has revealed himself to them by calling them to follow him. At the moment of their call, Jesus showed up their sin and made them aware of it. Complete truthfulness is only possible where sin has been uncovered, and forgiven by Jesus. Only those who are in a state of truthfulness through the confession of their sin to Jesus are not afraid to tell the truth wherever it must be told. The truthfulness which Jesus demands from his followers is the self-abnegation which does not hide sin. Nothing is hidden, everything is brought forth to the light of day.
In this question of truthfulness, what matters first and last is that a man's whole being should be exposed, his whole evil laid bare in the sight of God. But sinful men do not like this kind of truthfulness, and they resist it with all their might. That is why they persecute it and crucify it. It is only because we follow Jesus that we can be genuinely truthful, for then he reveals to us our sin upon the cross. The cross is God's truth about us, and therefore it is the only power which can make us truthful. When we know the cross we are no longer afraid of the truth. We need no more oaths to confirm the truth of our utterances, for we live in the perfect truth of God. ("The Cost of Discipleship" by Dietrich Bonhoeffer, pg. 138-139)
How clear this is, that only those who know Jesus Christ and have looked to the cross can be unafraid of truth. The cross, the place where we see the depths of the horror of our sin as we realize the cost of the atonement through the sacrifice of God's only Son, is a place of mockery for those who love their sin.
God's truth about us. What a heavy thing, for that truth reveals us as completely ugly, completely unworthy. And yet, where that sin is revealed, it is also atoned! This two-fold truth about sin and sanctification is the marvel of the cross, the crowning jewel of the revelation of God's truth, and the foundation of our faith. This is the truth Christ calls us to live in every day. I was really encouraged by this passage, and I hope you were too. :) Let us be encouraged that even when others revile us for clinging to the truth, it is for the sake of Christ.
"But if we walk in the light, as he is in the light, we have fellowship with one another,
and the blood of Jesus, his Son, purifies us from all sin." (1 John 1:7)