God is patient with the human race.

“The Lord is… patient toward you, not wishing for anyto perish but for all to come to repentance.”
2nd Peter 3:9 NASU

However, there is an end-point. Because Manasseh “killed innocent people... the Lord was unwilling to forgive.” 

Divine un-forgiveness is an un-common occurrence in the scriptures, but it happens. Thankfully, the Lord is “patient,” “merciful and gracious,” “longsuffering,” and “forgiving.” But there appears to be a limit to His willingness to overlook sin.