This is an extremely sad number. It's from the point of view of a desperate, depressed person, and his reasons for his woe are revealed somewhat... but never made perfectly clear.
The song starts with the same chord progression as "Earth Angel" and dozens of other songs from its era. The other thing we hear is a young, Pat Boone-rich, Johnny Mathis-creamy voice that I am very sad to say is not identified.
The lyrics open enigmatically: "Sitting here thinking what life's all about/... till I'm ready to shout./ I've lived a big lie and now I'm going to die."
Which is dramatic... but so far unspecific. The second verse has the speaker approached by someone he knows: "that man," about whom we only learn that he has a "smiling face."
This man has a task, namely escorting our speaker "to that place/ Where life's at an end and where there's not a friend to love."
At this point in the riddle, we are ready to guess an answer. The speaker is a convict. He has lied about something, and is now to be executed. The man's-- jailer's-- smile now seems much less benign, and much more sinister.
This seems extreme-- capital punishment is usually reserved for crimes of violence and murder. Most of the severest lies involve only, perhaps, embezzlement or fraud. But even the most big-time thieves only get life imprisonment. In this case, living a double life is costing his actual one. Were drugs involved? Murder by proxy? Treason?
We don't know. Perhaps the death penalty is being used here metaphorically; life imprisonment can seem like death, and a place "without a friend" might imply solitary confinement. Or perhaps the songwriter is ignorant of the legal code, or simply decided that jail wasn't dramatic enough for his poetic purposes.
In the bridge, we see that "die" might, in fact, have been an exaggeration all along: "I'm on my way to stay/ And when I'm gone I'll have pity and fear/ For those like me who never will be free." Oh, so it is life imprisonment?
Maybe... the line then is then completed: "...who never will be free/ Of a worthless life filled with sadness and strife." So, he will not be "free of [his] life." He will have to live with his misery...but not literally die.
It begins to dawn on the listener that the substance of the punishment is immaterial. The speaker is going to be punished for his lie of a life, either by dying for it or by a "living death" of lifetime incarceration.
The song ends twice. Once, with an Aesop-like device: "The moral of my song is easy to see/ Don't live a life like mine-- be happy and carefree/ Love and be loved, then life will be but a dream." This seems unnecessary. In a 30-second public service announcement, we might need to be told outright that only we can prevent forest fires. But here, this spelling-out of the theme is a bit egregious.
Then, this, tacked on to the very end: "O Lord, please forgive me." Well, now we have the title. But it's unclear as to whether he is asking the Lord for forgiveness, or if it's more of an "Oh Lord," an expression like "Oh dear," "Oh woe," or "Oh man."
Simon returned to this character, the repentant criminal, in "Wednesday Morning, 3AM" (and its remix, "Somewhere They Can't Find Me") but in a more specific, less bathetic and preachy way... making the song more effective. He gives the criminal a definite crime, full of detail. And he gives him a lady love to leave as he flies justice.
What hasn't changed is what the criminal most regrets. Not, say, having disappointed someone or having hurt someone or even having sinned. No, he regrets what might have been, had he not committed his crime.
Next Song: Wow Cha-Cha-Cha