1 Corinthians 7:35 (NIV)
35 I am saying this for your own good, not to restrict you, but that you may live in a right way in undivided devotion to the Lord.
Every married person can attest to this: once you are married, you are no longer looking out for just yourself. Now you have a spouse and possibly kids to be concerned about.
It's for this reason that Paul seems to prefer and encourage singleness for Christians in 1 Corinthians 7. It's not because marriage is sinful, but because practically speaking a single person has a lot more time and a lot less complicated life that he or she can devote to serving God.
So what does that mean for us? For single people, be busy about the Lord's affairs. Use the time and freedom you have right now to serve God with "undivided devotion" (v35). And if you desire to get married one day, trust the Lord that as you seek Him first and serve Him with undivided devotion, He will -- in His way and in His time -- provide the best partner for you, someone who also wants to serve God with undivided devotion. (Just like Adam who was busy going about God's work and one day God provided him with his partner while he was sleeping!)
If you are married, don't see your spouse and your family as a burden or a distraction from God's calling. Remember that they are your primary ministry. Do your best to model for your spouse and your family what Christ's love looks like in practice. Pray together and share God's Word with each other. Be committed as a family to serving God together. In so doing, you won't just be raising a family, but God will use you to raise disciples in your home and build His kingdom.
Praise God! Whether we're single or married, we are surrounded by opportunities to serve Him. Let's make the most of those opportunities and serve God with as much undivided devotion as possible.