Why should we continually ask forgiveness?
We should continually ask for forgiveness because we are always sinning through our deeds, our mind and so many things that we do, we do them without knowing that we are sinning. so we really need to continue asking for forgiveness.
How can unforgiveness on our part block God's blessing?
God normally does not bless those who do not forgive. Because the condition that God gave us is that we should forgive and its only then that our sins are also forgiven by him and from there HE CAN NOW ANSWER OUR PRAYERS AND BLESS US.
How can unforgiveness block God's forgiveness?
It is the condition which our God gave us. He new that if people will not be forgiving other people there will be chaos on earth. so, He thought it wise that people should first forgive their enemies before God forgive them. This allows peace to reign on earth.