The Root cause for weakness in faith is preoccupation with worldy life
The root cause for weakness in faith is preoccupation and obsession with the world and its affairs. Man runs after money, wealth, position and many other worldly things, and in the process neglects obeying Allah's commandments.
Allah says "Verily! We have made that which is on earth as an adornment for it, in order that We may test mankind as to which of them are best in deeds." (Quran 17:7).
The key to increase faith is stop being preoccupied with the world and give priority to Allah's commandments.
Therefore let us forsake the love of this world for the hereafter and make our focus to please Allah in everything we do and refrain from anything that displeases him.
Let us concentrate on our ultimate and final destination which is the hereafter and put more investment into the hereafter where we will spend eternity as oppose to this world where we can go at ANY second!