Existence is the coherence of manifested (man) and un-manifested (paramatma). Basic interactions happen at a man to man level with disregard to paramatma ; Krishna termed this as the path of demons (7.15). The next level of interaction is between man and paramatma. This transition starts as one gets tired of chasing mirages or is vexed by misery.
In this regard, Krishna says these interactions or worship between man and paramatma are of four types. The first category of worshippers want to remove their difficulties, the second want to attain wealth, success or peace of mind, the third want to attain knowledge and the fourth are Jnani (wise) (7.16).
He says that the first three, who are otherwise deprived of wisdom, approach different forms (Gods) to fulfil their desires (7.20). This is like consulting the concerned doctor based on ailments. He further says that when they worship with shraddha (trust with commitment), he (Krishna) makes that shraddha unflinching (7.21) and their desires get fulfilled because of their shraddha (7.22) but these three paths give limited results (7.23).
Firstly, this appears to run contrary to 'performing our karma without expecting the fruits of action (2.47)' which is the fundamental attribute of the eternal state. Out of compassion, Krishna is helping us with the gradual transition from evil or darkness to the bright light of the eternal state which is desireless.
Secondly, he says that their shraddha fulfils their desires and he is behind that shraddha. This implies that our shraddha in a relationship; towards God or towards work bestows due rewards to us. If we ever attained anything in the physical world it's because of the presence of our shraddha . Shraddha is the same dedication even in adverse situations where we need to have patience and that's why it is said ' shraddha with saburi (patience)'.