"Repent ye therefore, and be converted, that your sins may be blotted out, when the times of refreshing shall come from the presence of the Lord;" - Acts 3:19

Isaiah prophesied of this refreshing – 

"For with stammering lips and another tongue will he speak to this people. To whom he said, This is the rest wherewith ye may cause the weary to rest; and this is the refreshing: yet they would not hear." - Isaiah 28:11-12 

This refreshing is the Holy Ghost.  

"And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance." - Acts 2:4 KJV 

It is also our spiritual rest. 

"Come unto me, all ye that labour and are heavy laden, and I will give you rest. Take my yoke upon you, and learn of me; for I am meek and lowly in heart: and ye shall find rest unto your souls. For my yoke is easy, and my burden is light." - Matthew 11:28-30

We yoke ourselves together with Jesus when we covenant with Him by water baptism in Jesus name. With this covenant, our sins are blotted out. Isaiah prophesied of this – 

"I have blotted out, as a thick cloud, thy transgressions, and, as a cloud, thy sins: return unto me; for I have redeemed thee." - Isaiah 44:22  

With this covenant, He gives the promise of His Spirit, which brings rest unto our souls.

"Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost. For the promise is unto you, and to your children, and to all that are afar off, even as many as the Lord our God shall call." - Acts 2:38-39