There are four types of bhaktAs (those who worship) Arthin (one desiring sense objects), arthArthin (one desirous of wealth), jij~nAsu (one desiring knowledge) and j~nAnI.
The first two are lower type – loving the means rather than end. Here the end is not god but the some other desired entities based on rAga and dveSha – gaining which they are happy or getting rid of that they are happy – hence the end is not God but their love for God is only a means for their desired end. Hence they love the means to achieve the end. Most of the people go to the temple with a big list. What they love is not God but the fulfilment of their desires. Hence God is only a means to achieve the ends they want.
But, what they are seeking is happiness, which is Ananda, which comes only from the limitlessness that is God. However, here the love is love for the objects rather than God although what they are seeking is the lord only (as happiness) but they mistake it as happiness that is coming from objects.
VidyAraNya says – viShayAnande brahmAnandaH – the happiness that one enjoys through sense enjoyments is happiness that comes associated with the Lord. Although they are going after (worshipping) sense objects they are going after me. However, they are ignorant that I am the real source for happiness. They are worshipping me only as a means to achieve the sense enjoyments; thus their devotion is backed by the ignorance.
The next best bhaktAs are jij~nAasu-s. They are going after me to understand about my nature since here I am the end not the means. All the dvaita bhakti is essentially at this stage, even though dvaitins may want think otherwise.
The best of all the four is j~nAnI where the identity of oneself with the total self is recognized. The bhakti for the Lord is translated as the realization of the identity – since pure love has to terminate with identity. This is the ultimate bhakti since there is no more ego left to have any separateness of Him and me. Hence, Krishna says among all the four bhakta-s j~nAnI is the supreme, he loves me most, and I love him most, since one loves oneself the most. Hence, advaita is the result of bhakti where the mUlAvidyA that I am separate from Him gets resolved in that knowledge. Hence, this bhakti is backed by knowledge unlike the others.