Loving God means keeping his commandments, and his commandments are not burdensome (NLT).
This is a very impressive sentiment, one that is consistent with the general ethical perspective of John's epistle. It seems to me that John has a robust moralist perspective. It is relatively clear that for John, the ethical life of the Christian has significance for salvation. For example, our fellowship with God and with one another, as well as our benefiting from Christ's death, depends upon our walking in God's light (1.5-7). Likewise, our boldness and confidence before God in prayer depends upon our obeying his commandments (3.21-2). Finally, our boldness on the day of judgment is grounded in our living like Jesus did (4.17).
All this may be quite foreign to many of us, however, especially if we grew up or were theologically educated to think of the Law as an oppressive force, moralism as anti-gospel, and so on. And certainly it has to be at least a little uncomfortable for the person who is aware of her own sinfulness and propensity to fall short. Yet John doesn't apologize for his relatively strict stance. He says that God's commandments are not burdensome. Why is that?
It seems to me that, for John, the moral life of the Christian with all its difficulties—the sacrifice, the pain, the sufferings—is yet not burdensome because God has provided abundantly for our success. In other words, we are not fighting this battle alone; God is on our side and helping us all along the way.
God provides for us in these ways: Jesus his Son intercedes for us and forgives us our sins (1.5-10); his sacrifice stones for the sins of the whole world, including our own (2.1-2); we have been adopted into God's family, so we know that he treats us like his children (3.1); the "seed" of God planted in a person's heart grows into a whole new life, and keeps them from being overrun by sin (3.9); and finally, we have reminder after reminder that God loves us, because it is his very nature to love (4.7-10).
There is no denying, in my mind, that the human person has at least a partial responsibility for her own salvation, but this is always in response to and in cooperation with the gracious initiative of God. And it is always important for us not to be paralyzed by feelings of weakness or guilt or pride. We can do this by constantly reminding ourselves: This is real love—not that we loved God, but that he loved us and sent his Son as a sacrifice to take away our sins (1 John 4.10).