This is from Vladimir Lossky's book, The Mystical Theology of the Eastern Church (St. Vladimir's Seminary Press, Crestwood, New York, 1976). This excerpt appears near the beginning of Chapter Ten; in my edition, it begins on page 197.
The notion of merit is foreign to the Eastern tradtion. The word is seldom encountered in the spiritual writings of the Eastern Church, and has not the same meaning as in the West. The explanation is to be sought in the general attitude of Eastern theology towards grace and free will. In the East, this question has never had the urgency which it assumed in the West from the time of St. Augustine onwards. The Eastern tradition never separates these two elements: grace and human freedom are manifested simultaneously and cannot be conceived apart from each other. St. Gregory of Nyssa describes very clearly the reciprocal bond that makes of grace and free will two poles of one and the same reality: 'As the grace of God cannot descend upon souls which flee from their salvation, so the power of human virtue is not of itself sufficient to raise to perfection souls which have no share in grace ... the righteousness of works and the grace of the Spirit, coming together to the same place, fill the soul in which they are united with the life of the blessed.' ('De Instituto Christiano', P.G., XLVI, 289 C.)
Note (my own): St. Gregory does not mean God deprives anybody of His grace, but that some people do not want it and God will not force Himself upon them. But in the blessed, grace and works unite and together fill the soul. Lossky continues:
Thus, grace is not a reward for the merit of the human will, as Pelagianism would have it; but no more is it the cause of the 'meritorious acts' of our free will., For it is not a question of merits but of a co-operation, of a synergy of the two wills, divine and human, a harmony in which grace bears ever more and more fruit, and is appropriated - 'acquired' - by the human person. Grace is a presence of God within us which demands constant effort on our part; these efforts, however, in no way determine grace, nor does grace act upon our liberty as if it were external or foreign to it.
If you are not a theology buff, you'll probably be glad to stop reading right here. But if you like this sort of stuff, here's a bit more. The above paragraph continues:
This doctrine, faithful to the apophatic spirit of Eastern tradition, expresses the mystery of the coincidence of grace and human freedom in good workis, without recourse to positive and rational terms. The fundamental error of Pelagius was that of transposing the mystery of grace on to a rational plane, by which process grace and liberty, realities of the spiritual order, are transformed into two mutually exclusive concepts which then have to be reconciled, as if they were two objects exterior to one another. St. Augustine, in his attack on Pelagianism, followed the example of his adversary intaking his stand on the same rational ground, where there was no possibility of the question ever being resolved.