In another lifetime you two matched wits against each other and struggled to gain dominance over one another's ideas. You may have been quarreling friends or siblings, or the intellectual battle between you could have been larger-scale than that, such as two scientists whose important work and discoveries were diametrically opposed. You argued and pitted your mental strengths against each other in such a way that has carried over to this life.
You'll notice as you get to know this person that there's a feeling of intellectual competition between you, and you could even feel nervous about voicing your views to your lover for fear that they'll ridicule you. Alternatively, you could spend too much time with your partner talking about your past and effectively hindering your own ability to move, and think, into the future. Both of you are on a path of personal evolution, after all, and your focus should be on gaining new ideas, knowledge and insight. But if that's impossible, due either to that intellectual competitiveness or to focusing together too much on the past, you'll effectively be stagnating your own intellectual growth by being involved with this person.