The Word of God says, "Be ye holy, even as I am Holy". God is Holy! Above all and foremost, He is Holy! God has many attributes - great ones for us to follow, like Be merciful , Blessed are the meek, Blessed are the pure in heart, Blessed are the peacemakers (Mt.5), and then there are the Fruits of the spirit, which are love , joy, peace, patience, gentleness, goodness, faith, meekness, temperance. (Galatians 5) These all relate to Holiness- an inside type of Holiness, which we are to copy. Things which people cannot actually physically touch, but that they can feel. Others are affected in a positive way when Christians act out god's Holiness - when we try to clean up our lives inside.
Outward Holiness, which shows immediately, to others, is also great. It's good..its important! The Word talks about christians being an example to the believers and about being separate, not conforming to the world, not encouraging the lust of the eye in others by our clothing, or lack of clothing, presenting our bodies a living sacrifice (Romans 12) holy, acceptable unto God. We are to be set apart. We are to look different on the outside, than unbelievers. Holiness, must show on the outside. Holiness must affect what we buy , which others will view on our bodies. Holiness must say ," I will cover up my nakedness in public". God covered Adam and Eve, to cover their shame. Shame should exist in a Christian concerning outward modesty.
Actually, outward modesty isn't that hard. If it is hard to you, there's something much harder - it's inward Holiness - it's yielding to the abiding presence of the Holy spirit, so that the fruits of the Spirit can manifest themselves. It's a daily or hourly learning to know who God is and what He doesn't like that is presently inside of you. We read in the word of God examples of what God doesn't like..even HATES...envy, jealousy, gossip, maliciousness, slander, hatred, pride, haughtiness "I,m better than thou", greed, not caring to help the widows, the orphans, or the poor, lusting for your neighbour's things or lusting after their spouse, a pornographical spirit, arguing, debating to make contentions, etc. There's much we can read in the Bible which shows us the right thing to do. Then, the Spirit can bring it to our attention, daily, hourly.
As we get to know God - whose name is Jesus - and abide in the Spirit - which is the Spirit of God - we will be more sensitive to what is Holy and what is not Holy inside of us. We must be careful not to quench the Spirit as then soon, the sensitivity will grow dull.
Holiness - Be Ye holy, even as I am Holy - Both an inward and an outward concept. God wants us to be Holy, demands it of us, commands us to be Holy. Why? Because He really does love us and because we are to be an example of true Christianity.
Jesus is coming - Be Holy - It'll be worth it all in the end!