"You shall love the Lord your God with all your heart, and with all your soul, and with all your mind, and with all your strength." (Mark 12:30, from Deuteronomy 6:5, see also Luke 10:27).
In my reading I have come across a teaching attributed to Maimonides, that the command to love God can be acted on by meditating on the infinite love of God towards us:
I have loved you with an everlasting love. (Jeremiah 31:3)
In time, as we become more aware of God's love, our own love for God awakens. And so "You shall love the Lord your God" is not only a command, it is also a promise. Yes, that has been said of other commandments before. This, too, God will add to us.