And I will also take of them for priests and for Levites, saith the LORD. – Isaiah 66:21

Serve the LORD with gladness: come before His presence with singing. – Psalm 100:2

If the Lord has taken of us to be His priests and Levites, let us serve Him with great thankfulness and joy. If any people should be glad, I am sure it is those people that feel the aboundings of His mercy in forgiveness, having heard those glad tidings, as it were, from the lips of Jesus Himself. “Thy sins which are many are all forgiven thee: go in peace.” They have something always to stimulate their gratitude and regale them with sunshine. “I am very poor,” saith one, “but, never mind, poor as I am, I am not a drunkard or a swearer now; I feel weak and sickly in body, it may be (but) never mind that; I have not the burden of sin upon my soul.” Or “I am unknown, quite unknown. I have nobody to come and see me. Never mind that; I am known to God. I am poor and needy, yet the Lord thinketh upon me. My great wounds have been healed in Jesus’ precious blood.” Why, you have always cause to be glad, my dear brother and sister, if you have had your sins forgiven: you have a fountain opened in your soul of love to Christ and joy in God, quite as surely as there is a fountain open for the cleansing of your sin in the side of Jesus. Those that had some good principles instilled into them by early training or some sort of preparation to receive the gospel, may not feel their deep indebtedness to the wonderful working of the Spirit; but those of us who were steeped in sin, and hardened in heart, when we are saved must magnify the power of God, and moved by that feeling we must serve Him heartily with our whole spirit, soul, and body. A man that feels what grace has done for him cannot help throwing his whole soul into it. ~ C.H. Spurgeon

https://www.blueletterbible.org/comm/spurgeon_charles/sermons/0992.cfm