Have you had to wait for something, and it never came at the expected time? Has someone made you a promise, but it looks like it will never be fulfilled? Have you prayed to God in anticipation of something, but even though the answer came, it was not at your expected timing?
For years now, we have been told that the Lord is coming soon, but it looks like that day will never come. Some believers get weary while anticipating the Lord's return. As humans, we have the tendency to get weary and/or give up when our expectations are not forthcoming. However, God is not limited to this three-dimensional space because he lives in eternity where time does not exist, and that's why His timing is not the same as ours.
But as regards the Lord’s coming, it seems as though it is late based on human time. God does not want sinners to perish in their sins. So, in His goodness, He delayed His return so that sinners could come to repentance, then turn away from their wicked ways and turn to God. What we define as slackness is actually God being patient so that the sinner can come to the knowledge of the truth and be saved. Hell was not made for man but for the devil and his angels. God does not want you to be a part of the second death, so you should take advantage of God's goodness, repent from sin, and live for Him until He returns.

Dear Heavenly Father, thank You for Your goodness and patience with me and for waiting for me to come to the saving grace of Christ. I am sorry for all the times You reached out to me, but I refused to answer. I am sorry for taking advantage of Your goodness to continue in sin. Lord, I ask that You uphold me to the very end. I ask for grace so as not to be weary while waiting for Your return. Whether in death or alive to witness Your coming, help me reign in eternity with You. 
In Jesus's name I pray. Amen.