People are divided into five categories when it comes to performing Salaah

There are those who wrong themselves by failing to perform Wudu' perfectly, or pray at prescribed times of Salaah, ignoring its Arkaan (essential ingredients).
There are those who perform Salaah on time, make perfect Wudu', and maintain its Arkaan; however, they lose their concentration during Salaah (Khushu') by listening to Satan's whisperings.
There are those who perform Wudu' perfectly, concentrating during Salaah, but they constantly battle against Satan's whispering and insinuations, in order to prevent him from stealing their Salaah; these people are performing both Salaah and Jihaad against Satan.
There are those who perform Salaah with complete submission to Allah. After they have completed Wudu', their hearts have fully surrendered to the worship of Allah and they forget about worldly affairs.
There are those who perform Salaah with complete submission, sincerely focusing their hearts and minds on Allah, earing and loving Him as if they were looking at Him; Satan cannot whisper to them for they are contemplating their Lord. The difference between these people and others with regards to Salaah is far greater than the distance between the heavens and the earth. In short, they are closer to Allah in Salaah than at any other time.

The first type will be punished for their poor Salaah.
The second type will be held accountable for it.
The third type will have their sins forgiven for it.
The forth will be rewarded for it.
The fifth will become close to Allah, because they concentrate on Salaah with their hearts and minds; they subdue their desire' and Satan's whisperings.

There are three types of hearts

The first heart is empty of Eaman and of any kind of good; this is a dark heart, which Satan no longer whispers into, because he, may Allah curse him, has already taken it as a permanent abode, and has full control over it.
The second heart is illuminated with the light of Eaman, but there is still a certain level of desire within it, so Satan can whisper into it every so often. The Eaman of this heart fluctuates, it increases and decreases; sometimes it defeats Satan, whilst at other times it is defeated.
The third hears is full of the light of Eaman; there is no desire that can affect it. This type of heart is always shining with Eaman, so Satan's whispering cannot affect it; in fact Satan is likely be burnt as soon as he comes close to it. This heart is like the heaven, protected by the stars, so if Satan comes close to it he is stoned and burnt at once. This type of heart is protected by Allah because it is the focal point of Tawheed, love of Allah, knowledge and sincere Eaman. Such a heart is therefore deserving of protection from the allurement and ruses of Satan.