Continuance is a very important element in the spiritual life. It is easy for a person to begin a relationship with God, but, can he continue or not?! this is the question.
The Galatians "have begun in the Spirit" but they did not continue and concluded by the flesh (Gal. 3:3). Demas served with the Apostle Paul and did not continue "for Demas has forsaken me, having loved this present world. " (2 Tim. 4:10).
How easy it is to live a life of love for a certain period, but it is important to carry on, as the Lord said to the angel of the Church of Ephesus, "Nevertheless I have this against you, that you have left your first love. " (Rev. 2:4). And so the Lord said also, "Abide in My love. " (John 15:9).
To start is easy but the strength is to continue as St. Isaac said "An exercise which you do not practise steadfastly is fruitless."
If Satan finds out that you had begun a spiritual work, he will do his utmost to make you stop and not continue. Therefore, continuance in the spiritual action needs your seriousness, strong will and self-control...
Continuance shows the sincerity of your wish to live with God and also provides spiritual experience.
For if a person proceeds with a certain virtue, he will by time realise its scope, its wars and obstacles and how to overcome all this.
For the sake of continuance, the Lord said, "...he who endures to the end will be saved." (Matt. 10:22) because the good beginnings are not everything, their strength lies in that they carry on to the end unto death.
The Apostle said, "Remember those who rule over you, who have spoken the word of God to you, whose faith follow, considering the outcome of their conduct." (Heb. 13: 7). The greatness of those saints lies in their faithfulness to the end.
If you started a spiritual work and failed to continue, search for the reason. Perhaps you have begun with a level beyond your ability. In this respect the saints said, [little continuous work is better than a bigger one that stops after a time]...