God is love and the greatest commandments encompasses love. Jesus in the new testament, made the commandment into two. Which talks about love,

• Love God with all your heart, with all you might and all your soul
• And finally, Love your neighbour as yourself.

Jesus also said whatsoever you do to the lest of my brothers you do unto me.. Jesus is not a physical being so we can't show our love for him directly. But showing that love to your brothers and neighbours has already been recorded as Loving God your saviour.