Another one-liner:
“A pretty face don’t make no pretty heart”
– Moon Martin, “Bad Case of Loving You (Doctor, Doctor)”
Another They Might Be Giants:
Speak softly, drive a Sherman tank.
Laugh hard, it’s a long way to the bank.
From Rhythm Section Want Ad
I love how the OP specifically asked for two lines, and 6 of the first 21 responses offered one-liners. 
Mine:
She gave a little flirt, gave herself a little cuddle
But there’s no place here for the mini-skirt waddle
-Elvis Costello
Some more from Wilco
Took too long to see
I was wrong to believe in me only
–Solitaire
How to fight loneliness?
Smile all the time
–How to Fight Loneliness
No one wins but the thieves
so why side with anything
–Side With the Seeds
I was maimed by rock and roll
I was tamed by rock and roll
–Sunken Treasure
There are waters hidden from us, in the maze you’ll find them still;
I’ll take you to them, you take your young ones, may they take their own in turn.
“Testimony” Holly Near
I never was good looking
but now I’m too old to let that get me down.
Chris Smither, “Confirmation”
Losing love is like a window in your heart
Everybody sees your blown apart
–Graceland
These are the days of miracle and wonder
And don’t cry baby don’t cry
–The Boy in the Bubble
Here’s another one:
Poor man wanna be rich, rich man wanna be king,
And a king ain’t satisfied til he rules everything
Springsteen, Bad Lands
And, of course, everybody knows this one from The Who:
Meet the new boss
Same as the old boss
Won’t Get Fooled Again
Frank Zappa - The meek shall inherit nothing.
Those Jesus freaks, well they’re friendly but
The shit they believe has got their minds all shut
Mose Allison has a lot of pithy epigrams, such as:
Well I used to be troubled but I finally saw the light
I don’t worry about a thing because I know nothing’s gonna be all right.
Here is my nomination for shortest world philosophy in song lyrics, by Laurie Anderson:
Let X = X.
Move over, Luda’s got something to say
Do it now, 'cause tomorrow ain’t promised today.
- Ludacris, Stand Up!
Carly got it right:
It’s the stuff that dreams are made of
It’s the slow and steady fire
Heck, I could pull two-line philosophies from every song on that album:
“I know what I know
I’ll sing what I said”
“Breakdowns come and breakdowns go
So, what are you going to do about it, that’s what I’d like to know”
“People say I’m crazy, I got diamonds on the soles of my shoes
Well that’s one way to lose these walking blues”
“I want a shot at redemption,
Don’t want to end up a cartoon in a cartoon graveyard”
“This is the story of how we begin to remember
This is the powerful pulsing of love in the vein”
“Strong wind destroy our home
Many dead, tonight it could be you”
“I have no opinion about this
And I have no opinion about that”
“A long time ago, yeah, before you was born dude
When I was still single and life was great”
and my favorite:
“There’s no doubt about it, it was the myth of fingerprints
I’ve seen them all and man they’re all the same”
“And they say her flower has faded now, hard weather and hard booze
But maybe that’s just the price you pay for the chains that you refuse.”
Beeswing, Richard Thompson
“I’m from New Jersey, I don’t expect too much
If the world ended today, I would adjust.”
I’m From New Jersey, John Gorka
A one liner that I always liked…
“I am going to make it through this year if it kills me.”
This Year by The Mountain Goats.
Brendon Small
Bruce
Badlands
Yes! One of my favorite songs.
Also from Beeswing:
Ah, but I was so much older then
I’m younger than that now.
– Bob Dylan, My Back Pages