Question: How do I know if I have gained wisdom through Nianfo practice (mindfulness of the name of Amituofo)?
Answer: With your diligent Nianfo, do you have less suffering in everyday life now, compared with the past?
Q: Yes, suffering has lessened.
Q: How is less suffering related to more wisdom?
A: It is related as the practical function of wisdom is to lessen and eventually eradicate all suffering. All suffering arises from lack of wisdom (delusion or ignorance). As such, having less suffering means more wisdom arose, leading to more calmness, clarity and bliss of mind, which reduces suffering in everyday life. As Nianfo strengthens the connection between our unrealised Buddha-nature and Amituofo’s fully realised Buddha-nature, our wisdom towards that of the Buddha thus grows. (念佛开智慧) This is the reduction of suffering with wisdom.
Q: I see. But the wisdom I seek is to have a sharper mind now.
A: Depending on diligence and skill in Nianfo practice, there is usually, for the average practitioner, gradual, rather than sudden increase in wisdom. You just need to continue being diligent (or be more diligent) in Nianfo to experience sharper contrasts over time. Remember, as you have said, your suffering in life already did decrease through your Nianfo practice!
Q: Could the reduction of suffering be from another cause?
A: As Nianfo dilutes (to eradicate) our negative karma by creating more positive karma, or even pure karma (meritorious virtues; merits) through our self-power of expressing reverence to Amituofo, and through the other-power of Amituofo sharing his meritorious virtues (blessings) with us, our suffering reduces too. (念佛消业障) This is the reduction of suffering with compassion.