Grace is when we receive something we don't deserve. The Lord's grace is becoming heirs of the Kingdom of Heaven, even though we have sinned against Him. Through His mercy, by taking our punishment upon himself (2 Corinthians 5:21), He has paid our debt and made us heirs (Romans 8:7 & James 2:5) of His kingdom. Who does that? Our loving God is who does that. We must receive His grace through faith.
When we receive His grace we also receive peace, peace that our sins are not counted against us. These are our blessings we receive with our faith. This is a peace that surpasses all understanding (Philippians 4:7).
We truly grasp this grace and peace when we have knowledge of God through His Son, Jesus, the Christ. You see, just knowing about God, or that He exists, is not enough, we have to have knowledge of Him. That knowledge has the same idea of a husband and wife knowing one another. When the Bible speaks of a husband and wife coming together in physical union and a child is born of them, it is always said that the husband "knew" the wife, and a son is born. This is the same knowledge that Peter is talking of here. We are to know the Lord intimately, and we can. We can get to know the Lord in the same way we can get to know our husband or wife, we know them intimately, we know their likes and dislikes. We know what pleases them and what displeases them.
We can know the Lord the same way. How we get to know the Lord is by reading His word, the Bible. That is the Lord speaking to us, like a letter, or an e-mail, or instant messenger. We can respond back through prayer. These are two practices and disciplines of His followers who know the Lord and follow Him with all their heart. If you want to receive the Lord's grace and peace do likewise.