The specific word used for "love" here is that wonderful word "agape," which is the unconditional and unmerited love of God. It's not a love that comes naturally to us but is supernaturally given to us by the Holy Spirit (Romans 5:5). This agape love is to the Christian life what mortar is to a brick wall: without it, everything falls apart.
Notice that Paul combines this love with the exhortation for it to be "without hypocrisy." You might be interested to know that "hypocrisy" was actually a theatrical term back in biblical times. It literally means "wearer of the mask." It described actors who would pretend to be different characters by wearing masks portraying various features. We can be guilty of doing the same thing in the Body of Christ; we can put on a fake front by pretending to love others.
But pretend love is a contradiction of terms. God's agape love is, by very definition, genuine and sincere. It isn't two-faced; He doesn't tell us He loves us with His fingers crossed. If there's an element of that in us, if we're putting on a mask to disguise ourselves, then we aren't loving people with the love of God.
"Yeah, but you don't know how hard it is to be that way with so and so!" Oh, it's not hard-it's impossible! Again, it's not us drumming up this love within ourselves, but it's God pouring it out on us. We can't agape on our own. We need to ask, seek, and knock on the door of Heaven for it. But God always makes provision for His commands, and this is the greatest command of all.
Romans 12:9 9 Let love be without dissimulation. Abhor that which is evil; cleave to that which is good.