I have been thinking that "truth" is one of the most misunderstood words in the Bible, for we keep thinking about the "truth" in modernistic terms. But truth, truthfulness and embodying truthfulness are all interrelated within the biblical worldview.
And if you know Greek, check out Ephesians 4:15. The Greek does not literally say, "speaking the truth in love". Instead, it's "truthing in love", which means embodying and living out the truth in love!
"Speaking the truth" may be part of it, but there is so much more. If we only speak the truth without living it out in love, then we are quite hypocritical, aren't we? On the contrary, if we live out and embody God's truth and truthfulness in love, then what we say has credibility. Imagine that we can truly care for others, give them grace, and show them genuine love, then people can truly see some measure of who God really is.
I tend to think that what Christ did on earth was to embody God's truth in his life, suffering and death, and God vindicated him by raising him from the dead. I think Paul tried to follow Jesus' life pattern, and he asked his Christian communities to do likewise.