BETTER UNDERSTANDING OF ENGLISH: Much of the vocabulary of English has Latin origins, much of which came to English by way of French. Since Spanish is also a Latin language, you will find as you study Spanish that you have a better understanding of your native vocabulary. Similarly, both Spanish and English share Indo-European roots, so their grammar is similar. There is perhaps no more effective way to learn English grammar than by studying the grammar of another language, for the study forces you to think about how your language is structured. It's not unusual, for example, to gain an understanding of English verb tenses and moods by learning how those verbs are used in Spanish.
THE US HAS THE 5TH LARGEST SPANISH-SPEAKING POPULATION IN THE WORLD! There are over 35 million Spanish speakers in the US. Presently, over 40% of the population growth in the United States is among the Hispanic people!
CULTURAL UNDERSTANDING: While most of us (Pope John Paul II may be an exception 
) can't hope to learn the languages of more than one or two cultures other than that of our own, those that we can learn help us to learn how other people learn and think. Spanish also offers a wealth of literature, both modern and traditional.
LEARNING OTHER LANGUAGES: If you can learn Spanish, you'll have a head start in learning the other Latin-based languages such as French and Italian. It will even help you learn Russian and German, since they too have Indo-European roots and have some characteristics (such as gender and extensive conjugation) that are present in Spanish, but not English. I wouldn't be surprised if learning Spanish might even help you learn Japanese or any other non-Indo-European language, since intensively learning the structure of a language can give you a reference point for learning others.
FOR YOUR HEALTH: Learning another language helps to avoid memory related illnesses. Studies show that bilingual people have better memory motor skills as they age and are less prone to diseases such as Alzheimer's.
Learning another language can help you to GET A BETTER AND HIGHER PAYING JOB!!!
¡ES FÁCIL! Spanish is one of the easiest foreign languages to learn. Much of its vocabulary is similar to English's, and written Spanish is almost completely phonetic. Look at almost any Spanish word and you can tell how it is pronounced. As well, while mastering the grammar of Spanish can be a challenge, basic grammar is straightforward enough that you can have meaningful communication after only a few lessons.
WHERE DID “IT” COME FROM? The Spanish language developed from vulgar latin, with influence from Basque in the north and Arabic in the southern part of the Iberian Peninsula. Typical features of Spanish diachronic phonology include lenition (Latin vita, Spanish vida; Latin lupus, Spanish lobo), palatalization (Latin annum, Spanish año) and diphthongation of short E/O from vulgar Latin (Latin terra, Spanish tierra; Latin novus, Spanish nuevo; Latin tempus, Spanish tiempo; Latin ferrum, Spanish fierro and now hier ro). Similar phenomena can be found in most other Romance languages as well, especially after the fall of the Roman Empire in the 4th century AD cut out further linguistic influence of original Latin.