Is it truly wrong to calculate that by doing good i’ll create good in my life?

Holy book is not wrong, it is right and absolutely correct. A Master must state the truth, the associated benefits of being good or nice to others and he is doing that but people who are listening to that are not ordinary people. These truths were told by Jesus to chosen few – those 10-12 disciples. These were the one’s who were genuinely interested in teachings. These select few were real seekers and interested in the Truth rather than their business. These people probably could understood his teachings, rest did not otherwise why would he crucified at all?

Is desiring spiritual growth a selfish endeavour?

You may be thinking “How can I become unselfish despite being engaged in normal day to day activity?”. Tao of creation teaches the same. In brief – the trick is to be aware of your “self” all the time. When you become aware of your self and your awareness deepens the emotions like selfishness, anger, jealousy etc. just start vaporizing. Surrendering the fruit of Karma to the divine is another great way to become free from the burden of selfishness. Good of bad, whatever be outcome of your actions rooted in duty – are His. Choose what you want but do not mistake duty for selfishness.