Attention in prayers (salat) is obligatory for momineen

Verily, the hypocrites seek to deceive Allâh, but it is He Who deceives them.[] And when they stand up for As-Salât (the prayer), they stand with laziness and to be seen of men, and they do not remember Allâh but little.

(They are) swaying between this and that, belonging neither to these nor to those, and he whom Allâh sends astray, you will not find for him a way (to the truth - Islâm).

An-Nisa 143

Comment

After reading this verse ,i am of the view that just performing the elements of Salat (prayer isn't enough) we should have the proper feeling of standing in front of Allah,bowing before him.We should have a feeling that we are no one but humble servants of Allah.

It is not fair for us that while performing Salat (prayer),worldly affairs be running in our minds.If we cant concentrate probably its an indication of our weak faith.
Second that we come to know from this verse is that we should make zikr of Allah as much as we can to make Him pleased with us because it is a sign of hypocrites mentioned in the above verse that they do not make zikr of Allah but little.