At first it sounds like someone might be bossing us around in this poem. The first part of the opening line, "Tell all the Truth" has an authoritative vibe, like something a parent, teacher, or other "in-charge" person might say. It takes a minute, but we realize this speaker isn't so much bossing as philosophizing. He or she (it's never clear which) is thinking about the truth with a capital T, and what that means to us, fragile, sensitive humans that we are.
Think of the speaker as someone deep in thought, someone who has willingly surrendered the Xbox for the afternoon and is seriously contemplating the big-picture things in life. More than that, this person feels downright compelled to pass this advice along to us. Thanks for the tip, yo.