It's a simple title, but that one word – "Spring" – is loaded with associations. Spring is the season of rebirth and renewal of the natural world. For Christians it's also the time to celebrate Easter and the resurrection of Christ. Both of those aspects are clearly important to the speaker of this poem.
By connecting innocence and beauty to the season, our speaker also implies a necessary loss of that beauty and innocence. Spring, after all, is part of a cycle of seasons. So, while spring comes every year, it also has to give way each year to summer, and then to fall and winter, when all that growth and vibrancy vanishes for a while.