"Peace I leave with you; my peace I give you. I do not give to you as the world gives. Do not let your hearts be troubled and do not be afraid."
The Bible says it best, so we will just provide some useful passages.
"Now it is God who has made us for this very purpose and has given us the Spirit as a deposit, guaranteeing what is to come. Therefore, if anyone is in Christ they are a new creation; the old has gone,the new has come."
"If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness."
"You have heard that it was said, 'Love your neighbour and hate your enemy'. But I tell you: Love your enemies and pray for those who persecute you."
"For if you forgive men when they sin against you, your heavenly Father will also forgive you."
"But when you pray, go into your room, close the door and pray to your Father, who is unseen. Then your Father, who sees what is done in secret, will reward you."
"Love must be sincere. Hate what is evil; cling to what is good. Be devoted to one another in brotherly love. Honour one another above yourselves. Never be lacking in zeal, but keep your spiritual fervour, serving the Lord. Be joyful in hope, patient in affliction, faithful in prayer. Share with God's people who are in need. Practice hospitality.
"Bless those who persecute you; bless and do not curse. Rejoice with those who rejoice; mourn with those who mourn. Live in harmony with one another. Do not be proud, but be willing to associate with people of low position. Do not be conceited."
"A gentle answer turns away wrath, but a harsh word stirs up anger."
Some additional Bible readings useful for new Christians can be found at Bible Reading