Imam Ibn al-Qayyim al-Jawziyyah said:

"O you of little resolve, where do you stand upon this path? Adam found it difficult and Nuh lamented because of it, while Allaah’s Khaleel Ibraaheem was thrown into a pit of fire due to it. Isma’eel was laid upon his side ready to be sacrificed for its sake, and while upon it Yusuf was sold for a cheap price and then falsely cast into prison for many years. Zakariyah was sawed in half, and Yahya was slaughtered due to it. Ayyub suffered great distress, while Dawood cried copiously, and ‘Isaa cured the wretched poor of their diseases and walked with wild beasts due to it. And how many, how many forms of difficulty and hardship did the Messenger Muhammad (sallallaahu 'alayhi wa sallam) face while proceeding upon it – yet you live through amusements and distractions!"

[al-Fawaaid: Page 41]

Imam Ibnul Qayyim al-Jawziyyah (rahimahullah) said: 

“[Such a person] does not become disheartened by those who differ from and oppose him, as they are lesser in importance and significance, even if they might be greater in number, as some of the Salaf said: “Traverse the paths of the truth, and do not be discouraged by the small number of people who do the same.” Every time you feel disheartened by your being alone on this path, then look to those who came before you and strive to catch up with them, and turn away from everyone else, as they will not benefit you in the least with Allah. If you happen to see them somewhere along the path that you are upon, then do not turn to look at them, for if you do so, they will distract you and simply delay your progress.” 

['Madarij as-Salikin'; 1/21]

Ibn Qayyim al-Jawziyya (rahimahullah) said:

“Doubtless, a heart grows tarnished like brass or silver, and its polish is by remembrance, which may make it shine like a crystal mirror.  So when one neglects the remembrance it tarnishes, and when he returns it shines.  Since the heart is tarnished by two things- heedlessness and sin- it is polished by two things: remembrance and asking forgiveness.”