Adjectives provide additional information about a noun or a pronoun. But the adjective (ewig) is in most instances unimportant for understanding of the sentence. The adjective simply describes.
It is the ending (-e) hung onto the adjective which is required when the adjective precedes the word it modifies. The ending itself supplies guide information to help the reader (listener) understand the sentence; here the noun Liebe is marked with the -e as: feminine, singular, nominative.
The ending marks for the reader (or listener) how the noun following is to be interpreted: as the subject, the direct object, the indirect object, or possessive.