Sufyaan Ibn 'Abdillaah t said: "O Messenger of Allaah r, tell me something about Islaam of which I will not ask anyone else besides you (after that)." He r said: "Say: 'I believe in Allaah' and then be steadfast (upon that)." 
This hadeeth is proof that the servant is obligated, after having Eemaan in Allaah, to persevere and be steadfast upon obeying Him by performing the obligatory acts and avoiding the prohibited ones. This is achieved by following the Straight Path, which is the firm Religion, without drifting away from it to the right or to the left.
If a Muslim lived through Ramadaan and spent its days in fasting and its nights in prayer, and in that month he accustomed himself to doing acts of good, then he must continue to remain upon this obedience to Allaah at all times (after that). This is the true state of the servant (abd), for indeed, the Lord of the months is One and He is ever watchful and witnessing His servants at all times.
Indeed, steadfastness after Ramadaan and the rectification of one's statements and actions are the greatest signs that one has gained benefit from the month of Ramadaan and that he struggled in obedience. They are tokens of acceptance and signs of success.
Furthermore, the deeds of a servant do not come to an end with the end of a month and the beginning of another. Rather they continue and extend until one reaches death, for Allaah says: And worship your Lord until the certainty (i.e. death) comes to you. 
If the fasting of Ramadaan comes to an end, then indeed the voluntary fasting is still prescribed throughout the entire year, and all praise is due to Allaah. If standing in prayer at night during Ramadaan comes to an end, then indeed, the entire year is a time for performing the night prayer. And if the Zakaat-ul-Fitr comes to an end, then there is still the Zakaah that is obligatory as well as the voluntary charity that lasts the whole year. This goes the same for reciting the Qur'aan and pondering over its meaning as well as every other righteous deed that is desirable, for they can be done at all times. From the many bounties that Allaah has bestowed upon His servants is that He has placed for them many different types of acts of worship and He provided many means for doing good deeds. Therefore, the enthusiasm and the zeal of the Muslim must be constant and he must continue to remain in the service of his Master.
It is unfortunate to find some people performing worship by doing different types of righteous acts during Ramadaan they guard strictly their five daily prayers in the masjid, they recite the Quraan abundantly and they give in charity from their money. But when Ramadaan comes to an end, they grow lazy in their worship. Rather, sometimes they even abandon the obligations, both generally, such as praying in congregation, and specifically, such as praying the Fajr prayer!
And they (even) commit forbidden acts such as sleeping over the time of prayers, indulging in places of foolishness and entertainment, and mingling in parks, especially on the day of 'Eed! Obtaining help from these evils is only through the Grace of Allaah. Thus, they demolish what they have constructed and they destroy what they have established. This is an indication of deprivation and a sign of perdition. We ask Allaah for His safeguarding and protection!
Indeed, these types of people take the example of turning in repentance and ceasing from committing evil deeds as something specific and restricted to (only) the month of Ramadaan. So they stop doing these (good) acts when the month stops. Thus, it is as if they have abandoned sinning for the sake of Ramadaan, and not out of fear for Allaah! How evil are these people who do not know Allaah except in Ramadaan!
Truly, the success that Allaah grants His servant lies in the fasting of Ramadaan. And Allaahs assisting him to do that is a great blessing. Thus this calls for the servant to be grateful to his Lord. And this understanding can be found in Allaahs saying, after having completed the favor of the month of fasting:
"(He wants that you) must compete the same number of days, and that you must magnify Allaah (by saying Allaahu Akbar) for having guided you, so that you may be grateful to Him." 
So the one who is grateful for having fasted, he will remain upon that condition and continue to perform righteous deeds.
Indeed, the true manner of a Muslim is that of one who praises and thanks his Lord for having been bestowed the ability to fast and make qiyaam (night prayer). His condition after Ramadaan is better than it was before Ramadaan. He is more ready to obey, desiring to do good deeds and quick to implement the obligatory acts. This is since he has acquired benefit from this prominent institute of learning. It is that of one who fears for having his fast not accepted, for indeed Allaah only accepts from those who have Taqwaa.