Paul's suggestion to not marry vs Great Protestant Theologians Paul states:


  1 Cor: 27 Are you pledged to a woman? Do not seek to be released. Are you free from such a commitment? Do not look for a wife.


Yet, if we look at the great Protestant theologians: Charles Spurgeon, John Owens, John Calvin, Martin Luther; as well as modern days: John Piper, John MacArthur, Timothy Keller, Paul Washer -- they're all married.

Why is there this disparity between Paul's advice and the great thinkers in reformed theology?
The answer is in the verse just prior:


  Because of the present crisis, I think that it is good for a man to remain as he is. (NIV 1 Corinthians 7:26)


In other words, given the 'present crisis' marriage posed various difficulties.  The present crisis was the crisis of religious upheaval that would lead to great persecutions. In situations that call for potential martyrdom, a single life would release a person from the addition worries and fears about their close loved ones. Can you imagine a father's worry over wife and child, or a child's horror at seeing their mother killed? It would simply be better, in many ways, to be without family during those days.

On the other hand - and in support of Paul's application the the current crisis - if a person did not have a strong urge to be married (which is a special gift) even in days without 'crisis', there are benefits to a single life (verses 32-36). 

It's just not considered as 'necessary' to be a great leader. Moses and Peter and the majority of leaders in the Bible had wives - only few went without, just like today.