If there is inner purity, then one can have the vision of God. Now, despite trying so hard you are unable to see God because of some latent impurity in you. Man is a bundle of thoughts, pure and impure. Most of the time our minds are filled with physical, mental and spiritual desires. Just as you need to open your eyes to see the sun in the sky, so also you need to open your inner vision to see God. The inner vision is purified only when all the samskaras of the past are wiped away through meditation and other spiritual practices. Whatever you see is a reflection of your own inner world. Increase your sadhana, and all impurities, past impressions will automatically clear off. Do not lose faith in your abilities, instead increase your spiritual practices and you shall soon succeed in your mission.