Judas did no deny Christ. Judas betrayed Christ. He never denied knowing Christ. In fact, he betrayed Christ with a kiss. Peter denied Christ out of fear. Remember what Jesus said to Peter in Luke 22:31-32 "31 “Simon, Simon, behold, Satan has [
a]demanded to sift you
men like wheat; 32 but I have prayed for [
b]you, that [
c]your faith will not fail; and [
d]you, when you have [
e]turned back, strengthen your brothers.”:" Jesus prayed for Peter that his faith would not fail. Jesus went for Peter and showed Peter that his faith, while it faltered, it had not failed. Peter most certainly strengthened his brothers throughout the New Testament, to include the Epistles named after him.
Peter and Judas were not the same. Not even close. Judas fell apart because he knew he had betrayed the Son of God. Peter fell apart because he believed that his denial of Christ, in fear, was final. This is a good case study on how it isn't us that keeps our salvation, but God. While Peter believed and lived as though his denial of Christ meant his salvation was lost, Jesus pursued him and told him that his salvation was not lost.