“Teacher, which is the greatest commandment in the Law?”
Jesus replied: “‘Love the Lord your God with all your heart and with all your soul and with all your mind.’This is the first and greatest commandment. And the second is like it: ‘Love your neighbor as yourself.’ All the Law and the Prophets hang on these two commandments.” - Matthew 22: 36-40
I was initially surprised to know that Jesus would say something as the greatest commandment. I would think His answer would have been, 'OK all commandments are equally important, you have to obey everything'. However the actual understanding of why 'loving God' is the greatest commandment, points to a similar reason, it is the underlying reason that drives someone to obey everything that they can!
One way to understand the greatness or importance of this commandment would be to remove this for a second and then think about every other things that Bible says. We will find that the whole system fails without this command. None of the things would have any value without this. Love for God (because he first loved us) is the source for everything.
We can probably do many of the commands, but if its not based out of love for God we miss the whole point. For example whatever we do not out of love for God would lead us to idolatry. In 1 Corinthians 13 Paul says that even if we have the gifts of the holy spirit, or give our body for hardship, if we don't have love its all a waste.
Everything that we do should originate from love for God and man, it should continue in love.