In order to define sin, we must firstly clarify which is the aim or purpose of our transitory life.
The aim of our life is the acquisition of the Holy Spirit of God. As for fasts, vigils, prayer, almsgiving, and every other good deed performed for the love of Christ, these are merely the means of acquiring the grace of the Holy Spirit of God, it is not however the end result. All that is not performed for Christ’s sake, even though it be good, brings neither reward in the future life nor the grace of God in this life. That is why our Lord Jesus Christ said: “He who does not gather with Me, scatters”.
Acquiring is the same as obtaining – it has the same meaning as in “acquiring wealth”. Acquiring the Spirit of God is exactly the same but instead of gathering materialistic things, its effect is eternal happiness and blessedness.
Hence, sin means anything which distorts our path towards this target. The force of the sin capable to attract our mind from its eternal scope is felt by us as an earthy pleasure. This is the law of distortion.
We must avoid them by using all our force in a contrary sense with these evil forces which try to enslave us. Let us not make pact with the Devil, even if it seems so pleasant because then we will be enslaved eternally. We need the constant force of attention, humility and obedience in order to perform the good deeds needed to acquire the Holy Spirit.
Based on Saint Seraphim of Sarov, Elder Joseph of Vatopaidi
A candid shot from Divine Liturgy