It is both a personal separation and a collective separation. In battle, as well as in sports, there must be teamwork. How God's people need to learn this lesson. It is not a matter of what we can do as a Christian, it's a matter of what we give up for Him and His work. They Were Strong.
Physical strength is a prerequisite for both war and sport.
Spiritual strength is important for the soldier of Christ. Finally, my brethren, be strong in the Lord, and in the power of his might. Thou therefore, my son, be strong in the grace that is in Christ Jesus. They Were Serious. This was not a job for the frivolous nor the foolish.