Lyric discussion by RockStarJanine 

Cover art for G4L lyrics by Rihanna

I agree with earthsun and MIMl101 to a degree. To me the song is using "gangster for life" in association with the permanent scar that heartbreak and pain leaves on you emotionally and the bond between friends, in this case, sisterhood. Think about it. Gangs, the only way out is death or being rescued/saved away from it. The lyrics:

" You know I'm down for life Load it, reload it, lets go Gangster for life Til the day that I die. "

Her girls are there to back her up in the sense of being her backbone. They won't allow anyone to hurt one of their own or else there will be trouble, they'll stalk out the target, guns will be drawn as the lyrics say, but the hidden meaning is clear:

" I got these girls like a solider Trip and it's goin' down down down

I'm ready to roll Girl I'm with you If they get you they get me So come on let's go Bitch I'm with you if you whippin, you with me. "

and

" I promise I'll stand and fight Cause you know that I'm down. "

Song Meaning