For this is the love of God, that we keep his commandments. And his commandments are not burdensome. ~ 1 John 5:3 ESV
Love has a way of removing the burden from duty. We care for our children when they are sick, but we do not consider it a burden because we love them. Fidelity to our spouses is not onerous when we are in a loving relationship with them. We help our aging parents freely, because we love them. If we love God we do not consider obedience to him as burdensome. Instead of feeling that doing our duty is keeping us from what would make us happy, loving obedience confirms that we are being freed from the dictates of our own limited, fallen natures and can experience true happiness.