"We are bound to thank God always for you, brethren, as it is meet, because that your faith groweth exceedingly, and the charity of every one of you all toward each other aboundeth;" (2nd Thessalonians 1:3)

If man's exhibition of faith and show of love gained him merit before a holy God, then why did Paul not give man glory?

It is because faith and love are not the CAUSES of salvation. They are two of the most clear EVIDENCES of grace already dwelling in a child of God.

Jesus used very similar language:

"Verily, verily, I say unto you, He that heareth my word, and believeth on him that sent me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life." (John 5:24)

Jesus, the Savior Himself, clearly states that a person who believes already has everlasting life. This means that he has already been born again. To further emphasize this point, Jesus says that the person IS passed from death unto life. Belief is an evidence not a cause of the new birth.

Furthermore,

"We know that we have passed from death unto life, because we love the brethren. He that loveth not his brother abideth in death." (1st John 3:14)

In this passage, John, the Apostle of love, plainly teaches that love is also an EVIDENCE of new birth not a cause of salvation.

Having this clear understanding of cause and effect give glory to whom it is do - God and God alone.