Pippi posted a comment on my entry entitled Righteousness, and asked if "it is possible for one to slip out of the grace of God." To answer this question, we have to carefully look at what we mean when we say "grace of God." For many western Christians, the expression "grace of God" is used as a kind of synonym for salvation--salvation defined as going to heaven when you die. Within this paradigm, Roman Catholics and Protestants have many theories as to how one is saved by the grace of God, and most pivot on the question of will: divine or human. That is, is one saved by God's will (so that the human will has no role) or is one saved by one's choosing to be saved? Of course the arguments become quite convoluted because if one is saved by God's will, then the fact that a particular person wants to be saved is because God willed it that way. And if one is saved by choosing to follow Christ, then (to get back to Pippi's question) one can lose salvation by ceasing to follow Christ: can one "slip out of" the grace of God.
In Eastern Orthodox Christianity, human beings are always understood as free creatures. But freedom does not mean independence. All created things are dependent on the grace of God at all times. There is no existence apart from the grace of God, so it is indeed impossible to slip out of the grace of God, in one sense. In another sense, human freedom is such that God has given us the power to say "no" to Him. Still dependent on the grace of God on one level, human beings have the ability to reject the grace of God on another level.
Further, there is an experience often called the "withdrawal" of the grace of God testified to by many saints. This refers to an experience in which the manifest grace of God (the grace of God that one can experience and know) is (or seems to be) removed. This experience of the withdrawal of the grace of God is sometimes (but indeed not always) associated with a particular sin that seems to be the "cause" of the withdrawal of grace. However, the remedy for this condition is not merely repentance of a particular sin (if a particular sin is known, which is often not the case). The manifest grace of God returns only as one seeks God Himself, by faith, even when nothing at all is felt.
Salvation, as usually conceived in the Eastern Orthodox Church, is the restoration of the fallen image of God in the human being. From an Orthodox perspective this restoration requires the will of both God and man. It requires the work of both wills, the effort (or energy) of both. In the Orthodox Church we will often say that salvation is a matter of synergy (working together). Therefore, one cannot "slip" out of the grace of God, but one can nonetheless resist the grace of God--and God will allow you to do it. Salvation is a work of cooperation, a work of transfiguration that requires human desire, will, and participation. However, it is also a free gift, a miraculous work of God in our lives. It is a work of God that you have to accept, have to want, and have to cooperate with.
Salvation, for the Orthodox, is a process. It is not a decision by either God or a human being that settles the matter in a moment. It is a decision by both God and a human being that the human being must continue to make. God does not change. God wills, according to scripture and the teaching of the Orthodox Church, that all be saved. God's decision never changes. We are the fickle ones. Like children, we want to work with Dad in the shop--until we learn that Dad's work requires discipline, patience and self control. We want to be saved, we want to be like God (restored to the image of God that was undistorted in creation) until we realize that salvation means that we have to change. We have to become ourselves, we have to grow up, we have to shed childish ways to grow up into Christ.
And so our journey of salvation is seasonal. We draw near, we draw back. We are excited by the touch of God's manifest grace, we draw back because we fear change. We want to be mature in Christ, yet we don't want to control our minds and bodies. And God is merciful. God is patient. God as the loving Father lets us back into the shop to learn a little more, to try again, and does not hold on to us when we begin to resist. But His word is in our heart. Even when we are (or seem to be) far away, we feel a tug, we hear a gentle calling back, we have an unsatisfied longing. Prodigals are we all. The journey home is always longer and harder than we expect, but not nearly so long and hard as we deserve. And even before we reach home, our Father is running out to meet us.