What Does it Mean to be Eternal?

What does it mean to be eternal? People talk about "eternal life" frequently, but do we really understand this concept of eternality?

We are in fact eternal spirits that live in a body that gives physical expression on the earth to our spirit, and we are managed by our minds. We are spirit, mind, and body -- three distinct and three different components that comprise and function as one being, or one person.

We were made to be in form and in substance like our Creator. God is three persons, or three components who comprise one being, or one person. The Father who is God; the Son, Jesus, who is God; and the Holy Spirit God, who is God. In substance they are equal. In form and in function they are unique but they always agree completely.