Sri Chinmoy: No, sincerity can be fooled by the vital. Very often our sincerity is a slave to our vital. The vital can make the mind understand certain things in a very peculiar way. Your mind may tell you that if you do something in a certain way, that is the sincere way. But the vital can easily fool the mind and say, "No, this is not the sincere way. The other way is sincere."
We have to know where sincerity is coming from. If it is from the heart, then that sincerity will be helped by the soul's illumination. But if it is coming from the mind, the mind's sincerity is not reliable. The mind's sincerity is like an opportunist: I will be sincere to you if you do me a big favour, but if you do not do me a big favour, I am not going to be sincere. Very often mental sincerity acts like a first-class opportunist and the human vital is such a rogue. When the vital comes, it can easily change the mind's ideas, even if the mind has good intentions. The vital can change the feeling of sincerity that the mind has.
Sincerity itself is not enough for us to know if we are pleasing God. Sincerity is the first step. The second step is determination. Every day we can be sincere to ourselves. After having wrong thoughts, we can say, "I have wrong thoughts. I am recognising them; I am acknowledging them; I am making a confession that I have wrong thoughts, undivine thoughts, unhealthy thoughts and unaspiring thoughts. I am so sincere." But that is useless. True, we are behaving far better than others, who will not acknowledge or recognise their wrong thoughts. In our case at least we are ready to admit that we cherish wrong thoughts, undivine thoughts, vital thoughts. But then determination has to come. If determination is not there, you are not going to take the next step.
How many people recognise their wrong actions? Again, how many of those are determined not to repeat those actions? Only if determination comes can you go one step forward. Again, even if determination comes today, you may not be successful in changing your wrong thoughts or wrong actions. How many times does a child fall down before he can walk properly? In the very beginning he is sincerely trying to stand up and walk, but his sincerity is not enough. He needs determination. Otherwise if he falls down, he will give up. Again and again he has to show his determination.
In your case, in everybody's case, sincerity is absolutely necessary. It is of paramount importance, but it is not enough. You need determination as well. And even when you have determination, God's Grace is also necessary. Otherwise, determination itself can come from the vital, not from the psychic being or the soul. Vital determination says, "By hook or by crook, tomorrow I will become a good person." That does not work to transform your actions.
The only thing that works is God's Grace. You have to pray to God prayerfully and tearfully: "Give me the determination to change my life. Then I will be able to please You always in Your own Way." If you get determination from prayer or meditation, then that is real determination. Otherwise, in an aggressive way if you are bringing some thoughts or ideas into your being, that determination is no determination. Real determination has to come from tearful prayers or very profound meditation. If determination comes from these, only then can it change your life. Otherwise, sincerity alone is not enough, although it is better than insincerity.