Omnipotent is the attribute of God which describes His ability to do whatever He wills. God's will is only limited by His nature, therefore He cannot do anything contrary to His nature as God, such as to sin, to ignore sin, or to do something absurd or self-contradictory.
God is not controlled by His power, but has complete control over it. This means that if God says something will happen. He has the power to make sure that it will happen by only speaking it forth. When God promises eternal life to those who believe in the Lord Jesus Christ, He has the power to grant it.
Just as God cannot sin, He has the equal ability and power to forgive those who do.
Job 42:1-2 ESV Then Job answered the LORD and said: (2) “I know that you can do all things, and that no purpose of yours can be thwarted.
Jeremiah 32:17-18 ESV ‘Ah, Lord GOD! It is you who have made the heavens and the earth by your great power and by your outstretched arm! Nothing is too hard for you. (18) You show steadfast love to thousands, but you repay the guilt of fathers to their children after them, O great and mighty God, whose name is the LORD of hosts,
Jeremiah 32:26-27 ESV The word of the LORD came to Jeremiah: (27) “Behold, I am the LORD, the God of all flesh. Is anything too hard for me?
(For your extra reading on the greatest of God: Matthew 19:26; Genesis 17:1-8; Luke 1:37; Revelation 19:6)