Charles H. Spurgeon on Psalms 71:5

For thou art my hope, O Lord God. God who gives us grace to hope in him, will assuredly fulfil our hope, and, therefore, we may plead it in prayer. His name is "Jehovah, the hope of Israel" (Jer 17:13); and, as he cannot be a false or failing hope, we may expect to see our confidence justified. Thou art my trust from my youth. David had proved his faith by notable exploits when he was a youth and ruddy; it was to him a cheering recollection, and he felt persuaded that the God of his youth would not forsake him in his age. They are highly favoured who can like David, Samuel, Josiah, Timothy, and others say, "Thou art my trust from my youth."