The apostle Paul charges us to "pursue peace . . . and holiness." Pursuing anything requires the expending of energy; it is often very hard work. Pursuing holiness especially goes strongly against the grain of the carnal, anti-God nature residing within us, leftover from following the course of this world.
Further, Paul adds that we must pursue holiness because "without [it] no one will see the Lord." It is true that, while we are justified, we are also sanctified. Being set apart is an aspect of holiness. However, the responsibility of pursuing remains because God wants our holiness to be, not a static state, but a dynamic, living, practical, and working part of our character. This character is built through experience after we have been given access to Him. We must seek and build it through cooperative association with and because of Him and our Lord and Savior.
A number of motivations exist for doing so. The first - a no-brainer - is because we love Him. Jesus says in John 14:15, "If you love Me, keep My commandments." Another motivation springs from friendship. Jesus explains in John 15:14, "You are My friends if you do whatever I command you."
Do we want to please God? Jesus remarks in John 8:29, "I always do those things that please Him." Do we want to be in God's Kingdom enough to walk His way of life entirely, regardless of what God may demand of us? Joshua and Caleb did on the journey to the Promised Land. Jesus declares in John 17:4, "I have finished the work which You have given Me to do." He paid a huge price, and He made it.
We are told to pray without ceasing and to give thanks in every circumstance because both of these are part of God's will (I Thessalonians 5:17-18). We are also to study "to present [ourselves] approved to God, a worker who does not need to be ashamed" (II Timothy 2:15). Each of these is a labor that falls upon anyone who appreciates God for what He has done and for what He so generously and freely provides.
Do we want to witness for God, bringing Him glory by our labors of love? Is this not what all the heroes of faith in Hebrews 11 accomplished? According to Hebrews 12:1, they constitute a great cloud of witnesses. Abel's work of faith still speaks (Hebrews 11:4); Noah's witness condemned the world (verse 7), and Abraham's faith drove him to seek "the city . . . whose builder and maker is God" (verses 8-10). Hebrews 11:39 declares that all of those named or implied in the chapter obtained a good testimony through faith.
They worked in various ways, and they will be in the Kingdom. Undoubtedly, God included in His Book the witness of the shining examples of their labors so that their lives might prod us to do likewise in our own.