How should I interpret the word 'truth' in New Testament verses like Romans 1:18?

Les teaches that in the New Testament especially, whenever you see the word 'truth,' you can very easily substitute the name of Jesus Christ. This is because Jesus said in John's Gospel, 'I am the truth, the way and the life.' So in Romans 1:18, when it speaks of those who hold the truth in unrighteousness, it means they have taken the name of Jesus Christ and hold it down in ungodliness. They do not want anything He had to say or anything that comes from this Book; they hold it underfoot. Les suggests that whenever else you see the word 'truth,' try inserting the name Jesus Christ, and most of the time you will see what he is talking about. Then in verse 19, the truth is what may be known of God, manifest in them, because God has shown it to them. How? The invisible things of Him from the creation of the world are clearly seen, not in a fog or enigma, but as clear as a bell—the knowledge of the Creator God—being understood by the things that are made, even His eternal power and Godhead, so that they are without excuse. Les notes this is a hard verse because we have to think even back before Christ's time.