15      Do not love the world nor the things in the world. If anyone loves the world, the love of the Father is not in him.
16      For all that is in the world, the lust of the flesh and the lust of the eyes and the boastful pride of life, is not from the Father, but is from the world.
17      The world is passing away, and also its lusts; but the one who does the will of God lives forever.

4:7, 8 Here John resumes the subject of love for one’s brother. He emphasizes that love is a duty, consistent with the character of God. As has been mentioned previously, John is not thinking of love that is common to all men, but of that love to the children of God which has been implanted in those who have been born again. Love is of God as to its origin, and everyone who loves is born of God and knows God. He who does not love does not know God; for God is love. It does not say that God loves. That is true, but John is emphasizing that God is love. Love is His nature. There is no love in the true sense but that which finds its source in Him. The words “God is love” are well worth all the languages in earth or heaven. G. S. Barrett calls them:

4:9, 10 In the verses that follow, we have a description of the manifestation of God’s love in three tenses. In the past, it was manifested to us as sinners in the gift of His only begotten Son (4:9–11).

In the present, it is manifested to us as saints in His dwelling in us (4:12–16). In the future, it will be manifested to us in giving us boldness in the day of judgment.
First of all, then, we have God’s love to us as sinners. God has sent His only begotten Son into the world that we might live through Him and to be the propitiation for our sins. We were dead needing life, and we were guilty needing propitiation. The expression, “His only begotten Son” carries with it the idea of a unique relationship in which no other son could share. This makes the love of God all the more remarkable, that He would send His unique Son into the world that we might live through Him.
God’s love was not shown to us because we first loved Him. We did not; in fact, we were His enemies and hated Him. In other words, He did not love us because we loved Him, but He loved us in spite of our bitter antagonism. And how did He show His love? By sending His Son as the propitiation for our sins. Propitiation means satisfaction, place of mercy or a settling of the sin question.
Some liberals like to think of the love of God apart from the redemptive work of Christ. John here links the two as not being in the least contradictory. Denney comments:

4:11 John now enforces the lesson of such love on us: “If God so loved us, we also ought to love one another.” The if here does not express doubt, but rather is used in the sense of “since.” Since God so showered His love on those who are now His people, we also ought to love those who are members with us of His blessed family.
4:12, 13 God’s love is manifested to us at the present time in dwelling in us. The apostle says, “No one has seen God at any time. If we love one another, God abides in us, and His love has been perfected in us.” In John 1:18 we read: “No one has seen God at any time. The only begotten Son, who is in the bosom of the Father, He has declared Him.” In John’s Gospel we see that the invisible God is made known to the world through the Lord Jesus Christ. Here we have the expression “no one has seen God at any time” repeated in John’s Epistle. But now God is manifested to the world, not through Christ, for He has gone back to heaven and is now at the right hand of God. Instead God is now manifested to the world through believers. How stupendous that now we must be God’s answer to man’s need to see Him! And when we love one another, His love is perfected in us. This means that God’s love to us has achieved its goal. We are never intended to be terminals of God’s blessings, but channels only. God’s love is given to us, not that we might hoard it for ourselves, but that it might be poured out through us to others. When we do love one another in this way, that is proof that we are in Him, and He in us, and that we are partakers of His Spirit. We should pause to marvel at His dwelling in us and our dwelling in Him.

The things of the world may be desired and possessed for the uses and purposes which God intended, and they are to be used by his grace, and to his glory; but believers must not seek or value them for those purposes to which sin abuses them. The world draws the heart from God; and the more the love of the world prevails, the more the love of God decays. The things of the world are classed according to the three ruling inclinations of depraved nature. 1. The lust of the flesh, of the body: wrong desires of the heart, the appetite of indulging all things that excite and inflame sensual pleasures. 2. The lust of the eyes: the eyes are delighted with riches and rich possessions; this is the lust of covetousness. 3. The pride of life: a vain man craves the grandeur and pomp of a vain-glorious life; this includes thirst after honour and applause. The things of the world quickly fade and die away; desire itself will ere long fail and cease, but holy affection is not like the lust that passes away. The love of God shall never fail. Many vain efforts have been made to evade the force of this passage by limitations, distinctions, or exceptions. Many have tried to show how far we may be carnally-minded, and love the world; but the plain meaning of these verses cannot easily be mistaken. Unless this victory over the world is begun in the heart, a man has no root in himself, but will fall away, or at most remain an unfruitful professor. Yet these vanities are so alluring to the corruption in our hearts, that without constant watching and prayer, we cannot escape the world, or obtain victory over the god and prince of it.

New American Standard Bible: 1995 update. (1995). (1 Jn 2:15–17).