‘Hereby we know that we love the children of God, when we love God and do his commandments. For this is the love of God, that we keep his commandments. And his commandments are not grievous.'
And how will we know that we love our brothers? By the fact that we love God and obey His commandments, those commandments which show how we should live towards our brothers and the world, those which give the detail behind the commandment ‘you shall love your neighbour as yourself' (Matthew 19:19; Matthew 22:39; Romans 13:9-10; Galatians 5:14; James 2:8 - he calls it ‘the royal law'). If we fulfil these we are loving our brother in the way required. We note that the loving of our brother has now come within the wider commandments. God has not forgotten the world.
‘And his commandments are not grievous.' Here we are told that God's commandments are not ‘weighty, heavy to be borne'. The idea here is that they are not ‘burdensome' or ‘difficult'. As Deuteronomy 30:11-14 stresses, they are near and not far off. They are in their mouths and hearts, because they love God. Compare Matthew 11:30, ‘My yoke is easy and My burden is light'. In contrast Jesus spoke of the Pharisees in Matthew 23:4 as those who ‘bind heavy loads, hard to bear, and put them on men's shoulders.' So the reason that they are not burdensome is because we love God and delight to do His will, and because they are a response to God's love, carried in the heart, and not a way of earning it.