For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life. (John 3:16 kjv)
Love not the world, neither the things that are in the world. If any man love the world, the love of the Father is not in him. (1 John 2:15 kjv)
Why did St. John say we should love not the world whereas God is loving all and offering all eternal life and we are to walk in His Steps?
One may be quick to point out the issue of context here. But in my thoughts, I see that St. John clearly separated "the world" from "the things of the world". While he did not make this distinction in the Gospel, he made it clear that we should not love the things of the world in his epistle. In other words, why shouldn't we love the world which he had said God so loved while asking us to refrain from the materials things in it?
Additional Explanation: St. John seems to have differentiated between his use of "the world" and "the things of the world" in his epistle. It is clear that believers should not love the things of the world probably to avoid defilement. But, given that "the world" means "humankind" in John's Gospel, why does he urge the believers to not love the same "world" (humankind) which God himself loves?
As Eugene puts it:
why should man not love that which God himself loves. Why does God love the world? Whatever that reason is, why shouldn't man love it also for that reason?