How can 1 Corithians 15:3 and Psalms 49:7 be reconciled?

Easy: Jesus is both God and man! God can die for us in our place, like 1 Cor. 15:3 states.

3 For I delivered to you first of all that which I also received: that Christ died for our sins according to the Scriptures,

It would help if we read the Psalm in a little more context, rather than extracting a small snippet out of it. We need the back-story to understand what the context is. A little wider lens allows us to make sense of what God is teaching us in The Bible.

Psalm 49: 5-9 NKJV from BibleGateway

5 Why should I fear in the days of evil, When the iniquity at my heels surrounds me? 6 Those who trust in their wealth And boast in the multitude of their riches, 7 None of them can by any means redeem his brother, Nor give to God a ransom for him— 8 For the redemption of their souls is costly, And it shall cease forever— 9 That he should continue to live eternally, And not see the Pit.

The question is in verse 5. The answer to that question starts in verse 6, which is the key component here. Verse 7 refers to verse 6, as the reason that the rich can't save their brothers. It's not saying that "no man can die for the sins of another". Jesus died for all of us on the cross & rose from the grave 3 days after that!

Jesus died for our sins, because He is God & He has no sin. He had to become a man, so that He could be nailed to a cross. It's kind of impossible to nail a spirit - for example, an angel which doesn't have a physical body - to a cross. So God had to take on flesh to make that possible & to save us!

No one can give God a ransom for anyone as Psalm 47:7 says. The key statement here is "No one can give God a ransom" and the key word is Give

Only God can provide a ransom for Himself, as is evident from the story of Abraham.

Gen 22:8 And Abraham said, My son, God will provide himself a lamb for a burnt offering: so they went both of them together.

Even clearer,

Job 33:23,24: If there be a messenger with him, an interpreter, one among a thousand, to shew unto man his uprightness: Then he is gracious unto him, and saith, Deliver him from going down to the pit: I have found a ransom.

God found a ransom for Himself in Christ! I have found a ransom.

In context the scripture reads -

Ps. 49:6-9: “Those who are trusting in their means of maintenance, and who keep boasting about the abundance of their riches, not one of them can by any means redeem even a brother, nor give to God a ransom for him; (and the redemption price of their soul is so precious that it has ceased to time indefinite) that he should still live forever and not see the pit.”

Therefore, in context, no 'imperfect human' can provide the means to deliver someone else from sin and death. His money cannot buy eternal life, and his soul laid down in death, being the wages that are to come to him anyway because of sin, has no value toward delivering anyone.

“In Adam all are dying,” said the apostle Paul. (1 Corinthians 15:22) The ransom thus had to involve the death of the exact equal of Adam—a perfect human. (Romans 5:14) No other kind of creature could balance the scales of justice. Only a perfect human, someone not under the Adamic death sentence, could offer “a corresponding ransom”—one corresponding perfectly to Adam. (1 Timothy 2:6) It would not be necessary for untold millions of individual humans to be sacrificed so as to correspond to each descendant of Adam. The apostle Paul explained: “Through one man [Adam] sin entered into the world and death through sin.” (Romans 5:12) And “since death is through a man,” God provided for the redemption of mankind “through a man.” (1 Corinthians 15:21)

God arranged to have a perfect man voluntarily sacrifice his life. According to Romans 6:23, “the wages sin pays is death.” In sacrificing his life, the ransomer would “taste death for every man.” In other words, he would pay the wage for Adam’s sin. (Hebrews 2:9; 2 Corinthians 5:21; 1 Peter 2:24) This would have profound legal consequences. By nullifying the death sentence upon Adam’s obedient offspring, the ransom would cut off the destructive power of sin right at its source.—Romans 5:16.