Intentional and Unintentional Sins

Does it make a difference if we sin unintentionally or intentionally? The Elder Paisios says that the "errors we fall into through carelessness are of a less serious nature."  He adds that sins are sins, but there can be extenuating circumstances. When we fall into sin unintentionally God in His mercy will help us so that this fault can be used of some good purpose.
He explains,

This means that since we erred unintentionally, God simply utilizes our fault for some good. But when we plan ahead and err knowingly and then repent, we should also pray that no other harm occur from the consequences of our fault.

Some of us may face more temptations than others.  God will have mercy in such cases.
The Elder says,

Someone, for example will set off for somewhere without having any intention of committing a sin, but on his way he is tempted and falls into some sin.  He repents, struggles to avoid sin, but is tempted again. Such a person has extenuating circumstances, because he does not want to commit a sin, but succumbs to temptation and then repents. But who ever says, "If I am to achieve that goal, I must do wrong," and so forth, that person is sinning on purpose and intentionally. In other words he plans and lays out his scheme to sin in cahoots with the devil. This is especially evil because its premeditated... Such a person should never expect to be helped, because he does not deserve divine help, he will in all likelihood die unrepentant.

Some people say they can wait until they are on their sick bed to confess their sinfulness. Those with intentional sins are not likely to carry out this plan. The elder tells a story about a contractor who had such an idea.

The contractor said,"When I grow old, I'll go to the Holy Land and be baptized in the river Jordan to have all my sins washed away," and he continued to live a sinful life. Finally when he had no more energy and could barely walk, he said to his trusted worker, "I've decided to go to the Holy Land and be baptized in the River Jordan as a pilgrim." And the worker gave him a bold response, "Boss, if you're clean of heart you will go, but if you are not, you will die on the way!" It was like a prophesy! As soon as he arrived in Athens to prepare his papers, he died! Others took all of his money and made arrangements with a funeral home to have him sent back to his hometown in a coffin.

A life of repentance generally implies that we are trying not to sin and avoid intentionally sins.  We go to confession regularly to confess our sins that were due to the many temptations we faced.  We can be assured that God will be merciful if our intentions are pure. But those who intentionally sin thinking they can repent later may not find the same help from God. Just the thought of putting off Confession or participation in Holy Communion might imply that we are comfortable with out sins, our way of life, and do not need God's help.  This implies that we are willingly sinning.  To live a life of repentance called for by Christ demands a constant attention to all our sins. If we are and participate in the Sacraments regularly we will find God's love and mercy. He will then become our helper to guide us to salvation.

Reference: Elder Paisios of Mount Athos Spiritual Counsels III: Spiritual Struggles, p 132