http://chinesenotes.com/liji/liji019.html

人生而靜，天之性也；感於物而動，性之欲也。物至知知，然後好惡形焉。好惡無節於內，知誘於外，不能反躬，天理滅矣。
It belongs to the nature of man, as from Heaven, to be still at his birth. His activity shows itself as he is acted on by external things, and developes the desires incident to his nature. Things come to him more and more, and his knowledge is increased. Then arise the manifestations of liking and disliking. When these are not regulated by anything within, and growing knowledge leads more astray without, he cannot come back to himself, and his Heavenly principle is extinguished.

人生而靜
人 = rén = person, human, human being
生 = shēng = birth, born, alive, exist
而 = ér = and, then, implies sequential/causal relationship
靜 = jìng = quiet, still, motionless

天之性也
天 = tiān = heaven
之 = possessive
性 = xìng = (innate) nature
也 = yě = also

Paraphrase: Humans are born with a peaceful, qentle nature. The nature of Heaven is also like this.